A fractionation unit, method and use in a catalytic cracking or catalytic pyrolysis process

Abstract

The present invention provides a fractionation device, method and use in a catalytic cracking or catalytic pyrolysis process. The fractionation device includes a fractionation tower, a feed unit, a bottom tower oil unit and a recycle oil unit; the feed unit includes a reaction oil and gas feed pipeline and a fresh feed pipeline; the bottom tower oil unit includes first and second branch pipelines of the bottom tower oil; the recycle oil unit includes a recycle oil storage device, first, second and third branch pipelines of the recycle oil, and the three branch pipelines are respectively connected to a reaction device, the fractionation tower and a pipeline for extracting raw materials for preparing needle coke. By improving the fractionation device and process, the present invention raises the gas phase temperature above the chevron baffle, enables the components suitable for preparing needle coke to enter the recycle oil, solves the problems of ash content and carbon residue existing when using slurry as raw material from the source, helps to simplify the device and process and reduce costs; diluting the slurry with fresh feed can avoid the problem of easy coking at the bottom of the fractionation tower and ensure the long-term stable operation of the fractionation tower.

Description

Technical Field

[0001] The present invention belongs to the technical field of petrochemical industry, and relates to a fractionation device, method and use in the catalytic cracking or catalytic pyrolysis process. Background Art

[0002] In the process of petroleum processing, starting from crude oil, various feedstock oils will be produced, such as distillate oil, residue oil, hydrocracking tail oil, etc. The devices for catalytic cracking or catalytic pyrolysis using one or more of the above components as raw materials are fluid catalytic cracking (FCC) devices or catalytic pyrolysis (DCC) devices respectively, which are commonly used reaction devices in the petroleum processing process. Their products are mainly gaseous products, gasoline and diesel, and slurry and coke belong to by-products. The component between diesel and slurry is recycle oil. However, recycle oil is generally all recycled and converted and is not sent out of the device as a product.

[0003] Needle coke is a carbon material and can be used in the production of high-power electrodes, anode materials for lithium-ion batteries, and oil-based carbon fibers. According to the different sources of preparation raw materials, needle coke is divided into two categories: oil-based and coal-based. Among them, oil-based needle coke is processed from refinery heavy oil, that is, using the slurry component produced by petroleum processing as the raw material, which is more widely used and has a large demand, but the current production capacity is insufficient. In the actual production of needle coke, there are two major difficulties in raw material refining and coking process control. The former is because the slurry system has complex components, contains trace amounts of catalyst powder, has a high ash content and a high residual carbon content, which is likely to have an adverse impact on the quality of subsequent products. Therefore, pretreatment is required.

[0004] At present, generally, pretreatment devices such as solid removal and residual carbon removal are used to pre-treat the slurry. In the pretreatment process of the slurry, adding devices such as solid removal will increase the investment and operating costs, and generally there will be residues containing catalyst powder discharged, and their treatment is relatively difficult. The yield of the raw material for preparing needle coke obtained thereby is only about 80%. CN 106147835A discloses a combined method for separating catalytic cracking slurry and preparing oil-based needle coke. This method uses C3-C5 light hydrocarbon fractions as extraction solvents to perform subcritical or supercritical extraction on catalytic cracking slurry, makes the obtained extraction oil phase into extraction components through supercritical solvent recovery, uses the extraction components as the raw material for preparing mesophase pitch, prepares mesophase pitch through thermal polycondensation reaction, and then prepares high-quality oil-based needle coke through delayed coking reaction; although this method also involves the pretreatment of catalytic cracking slurry, its focus is still on the preparation process of needle coke, which belongs to the traditional process of preparing needle coke with slurry as the raw material, and still has the disadvantages of slurry pretreatment.

[0005] CN 111321004 A discloses a catalytic cracking fractionation tower slurry circulating heat extraction system, which includes a fractionation tower. The slurry outlet at the bottom of the fractionation tower is connected to a slurry discharge pipe, on which a slurry pump is provided. The outlet of the slurry discharge pipe is connected to the inlet of a first heat exchanger. The outlet of the first heat exchanger is respectively connected to the up-return and down-return tower slurry pipes and the external-slurry discharge pipe. The outlets of the up-return and down-return tower slurry pipes are respectively connected to the up-return and down-return tower slurry inlets of the fractionation tower, and the outlet of the external-slurry discharge pipe is connected to the tank farm. The return-refined oil outlet of the fractionation tower is connected to a return-refined oil discharge pipe, on which a return-refined oil pump is provided. The outlet of the return-refined oil discharge pipe is connected to the inlet of a second heat exchanger. This system belongs to the conventional fractionation tower and the connecting pipelines of its slurry and return-refined oil. By setting the heat exchanger, the coking problem caused by too high bottom temperature of the tower is solved. If it is used for preparing needle coke, it is still a process using slurry as raw material.

[0006] In summary, for the fractionation units of catalytic cracking or catalytic pyrolysis, currently, the slurry component is used as the raw material to prepare needle coke. Due to the characteristics of the slurry component, operations such as pretreatment are required, and there is no direct access to fractionated oil with basically no ash and carbon residue from the source, thus simplifying the production process of needle coke and reducing costs. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a fractionation device, method and use in the process of catalytic cracking or catalytic pyrolysis. By improving the fractionation device of the catalytic cracking or catalytic pyrolysis reaction products and improving the fractionation process, the components suitable for producing needle coke in the oil and gas enter the return-refined oil, solving the problems of ash and carbon residue existing in the traditional process using slurry as raw material from the source, eliminating the need for pretreatment, and reducing the subsequent equipment and production costs. At the same time, using fresh raw materials as the dilution component of the slurry to avoid coking at the bottom of the fractionation tower and ensure the long-term stable operation of the fractionation tower.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a fractionation device in the process of catalytic cracking or catalytic pyrolysis. The fractionation device includes a fractionation tower, a feed unit, a bottom oil unit and a return-refined oil unit. The feed unit is connected to the lower inlet of the fractionation tower, the bottom outlet of the fractionation tower is connected to the bottom oil unit, and the middle outlet of the fractionation tower is connected to the return-refined oil unit;

[0010] The feed unit includes a reaction oil-gas feed pipeline and a fresh feed pipeline; the bottom tower oil unit includes a first branch pipeline of the bottom tower oil and a second branch pipeline of the bottom tower oil. The first branch pipeline of the bottom tower oil is connected to a fluid catalytic cracking unit or a catalytic pyrolysis unit, and the second branch pipeline of the bottom tower oil is connected to the bottom tower oil reflux port of the fractionating tower; the recycle oil unit includes a recycle oil storage device, a first branch pipeline of the recycle oil, a second branch pipeline of the recycle oil, and a third branch pipeline of the recycle oil. Among the branch pipelines separated from the recycle oil storage device, the first branch pipeline of the recycle oil is connected to a fluid catalytic cracking unit or a catalytic pyrolysis unit, the second branch pipeline of the recycle oil is connected to the recycle oil reflux port of the fractionating tower, and the third branch pipeline of the recycle oil is a pipeline for extracting the raw material for making needle coke.

[0011] In the present invention, for a fluid catalytic cracking unit or a catalytic pyrolysis unit used in the petroleum processing process, the oil-gas products obtained by the reaction are fractionated to obtain various products. In traditional fractionating devices, the treatment of bottom tower oil slurry is emphasized, and needle coke is prepared with this as the raw material. However, at this time, the solid content and carbon residue of the oil slurry are relatively high, and the subsequent preparation process is complex. In the present invention, the fractionating device is improved, the temperature in the recycle oil extraction area is increased, the components suitable for preparing needle coke enter the recycle oil, the output of the recycle oil is increased, and at this time, the solid particles and carbon residue are still in the oil slurry and basically do not enter the recycle oil, reducing the difficulty of preparing needle coke with the recycle oil subsequently, helping to simplify the device and process, and reducing the production cost; since the output of the oil slurry is reduced, fresh feed is used in the present invention to dilute the oil slurry, avoiding the problem of easy coking at the bottom of the fractionating tower, ensuring the long-term stable operation of the fractionating tower, and using this mixed feed to exchange heat with the oil-gas, ensuring the temperature in the recycle oil extraction area, and washing the solid particles and carbon residue carried in the oil-gas to avoid their entry into the recycle oil, ensuring the quality of the recycle oil; the structure of the fractionating device is changed less, but the improvement effect is remarkable, the cost is low, and the applicable range is wide.

[0012] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0013] As a preferred technical solution of the present invention, a herringbone baffle is provided in the lower part inside the fractionating tower, and trays are provided in the middle and upper parts.

[0014] Preferably, the number of trays in the fractionating tower is 26 - 32 layers, such as 26 layers, 27 layers, 28 layers, 29 layers, 30 layers, 31 layers or 32 layers. The selection of the number of trays is related to the scale of the fractionating tower and the processing capacity of the oil-gas.

[0015] Preferably, the area connected to the recycle oil unit includes the 1st - 5th trays, that is, the extraction and return of the recycle oil are located within the above tray area.

[0016] Preferably, a gas-lifting extraction bucket is provided on the tray for extracting recycle oil.

[0017] In the present invention, by providing a gas-lifting extraction bucket on the extraction tray, all the cooled recycle oil components can be collected, thereby increasing the recovery rate of the recycle oil.

[0018] Preferably, the reaction oil and gas feed pipeline in the feed unit is connected to the inlet of the fractionating column below the chevron baffle.

[0019] Preferably, the fresh feed pipeline is divided into two branches, one connected to the bottom of the fractionating column and the other connected above the bottom of the fractionating column, with its inlet located below the inlet of the reaction oil and gas feed pipeline.

[0020] In the present invention, the fresh feed is added in two paths, replacing the original functions of the bottom cooling slurry and the stirring slurry in the column. The former is mixed with the liquid phase condensed by the chevron baffle in the fractionating column as a cooling medium, and the latter is directly introduced into the bottom of the fractionating column.

[0021] As a preferred technical solution of the present invention, the bottoms unit further includes a bottoms transfer pump. The bottom outlet of the fractionating column is connected to the inlet of the bottoms transfer pump, and the outlet of the bottoms transfer pump is connected to a bottoms branch pipeline.

[0022] Preferably, a bottoms heat exchanger is provided on the second bottoms branch pipeline.

[0023] Preferably, the bottoms heat exchanger is mainly a cooler, and the cooler includes a steam generator or a heat exchanger.

[0024] In the present invention, the installation of the bottoms heat exchanger is mainly to remove the excess heat at the bottom of the column and control the bottom temperature.

[0025] Preferably, the bottoms reflux port connected by the second bottoms branch pipeline is located between the chevron baffle and the tray.

[0026] In the present invention, the gas phase temperature above the chevron baffle is controlled by the flow rate and temperature of the mixed feed returned to the fractionating column through the second bottoms branch pipeline, so as to increase the heat load of the recycle oil section in the fractionating column and facilitate heavier components to enter the recycle oil unit.

[0027] Preferably, the bottoms unit further includes a third bottoms branch pipeline, and the third branch pipeline is connected to an emergency blowdown unit.

[0028] As a preferred technical solution of the present invention, the middle outlet of the fractionating column is connected to a recycle oil storage device through a recycle oil extraction pipeline.

[0029] Preferably, the recycle oil unit further includes a recycle oil transfer pump. The outlet of the recycle oil storage device is connected to the inlet of the recycle oil transfer pump, and the outlet of the recycle oil transfer pump is connected to a recycle oil branch pipeline.

[0030] Preferably, a recycle oil heat exchanger is provided in the recycle oil branch pipeline. The first recycle oil branch pipeline does not pass through the recycle oil heat exchanger, and the third recycle oil branch pipeline passes through the recycle oil heat exchanger.

[0031] Preferably, the second recycle oil branch pipeline is further divided into two branches. One branch passes through the recycle oil heat exchanger, and the other branch does not pass through the recycle oil heat exchanger. The branch pipeline passing through the recycle oil heat exchanger is connected to the cold recycle oil inlet of the fractionation tower, and the branch pipeline not passing through the recycle oil heat exchanger is connected to the hot recycle oil inlet of the fractionation tower.

[0032] In the present invention, after the heat load of the recycle oil section of the fractionation tower is increased, it is necessary to use the cold recycle oil returning to the tower after heat exchange of the recycle oil to remove the excess heat. Generally, the cooled recycle oil returns to the 4th tray. The temperature and flow rate of the cooled recycle oil determine the heat extraction amount of the recycle oil.

[0033] Preferably, a raw material heat exchanger for making needle coke is further provided on the third recycle oil branch pipeline.

[0034] In a second aspect, the present invention provides a fractionation method in a catalytic cracking or catalytic pyrolysis process. The fractionation method is carried out using the above fractionation device, and includes the following steps:

[0035] (1) Fractionating the oil-gas product after the catalytic cracking reaction or catalytic pyrolysis reaction in a fractionation tower to obtain slurry oil and recycle oil;

[0036] (2) Mixing the slurry oil obtained in step (1) with fresh raw materials and then dividing it into at least two parts. One part is used as the feed of the catalytic cracking unit or catalytic pyrolysis unit, and the other part returns to the fractionation tower to exchange heat and wash with the oil-gas product in step (1);

[0037] (3) Dividing the recycle oil obtained in step (1) into three parts. One part returns to the catalytic cracking unit or catalytic pyrolysis unit for reaction and recycling, another part returns to the fractionation tower as a cooling medium to condense the oil-gas product, and the last part is taken out as the raw material for making needle coke.

[0038] As a preferred technical solution of the present invention, the catalytic cracking reaction is carried out in a catalytic cracking unit, preferably a fluid catalytic cracking unit.

[0039] Preferably, the catalytic pyrolysis reaction is carried out in a catalytic pyrolysis unit.

[0040] Preferably, the composition of the oil and gas product in step (1) includes dry gas, liquefied gas, gasoline, diesel oil, recycle oil, and slurry oil.

[0041] Preferably, the oil and gas product in step (1) successively passes through the chevron baffle area and the tray area in the fractionating tower.

[0042] Preferably, the liquid phase condensed in the chevron baffle area enters the bottom of the tower to form slurry oil.

[0043] Preferably, the temperature of the gas phase after passing through the chevron baffle area is 300-420 °C, such as 300 °C, 320 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C or 420 °C, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 340-400 °C.

[0044] In the present invention, the control of the temperature above the chevron baffle will determine the yield distribution of recycle oil and slurry oil. When the temperature above the chevron baffle is high, the recycle oil yield is high, but the gas phase temperature above the chevron baffle shall not cause secondary cracking and result in changes in the oil product yield.

[0045] Preferably, the components with an atmospheric distillation range below 500 °C in the oil and gas product in step (1) rise to the tray area of the fractionating tower in a gaseous state, such as 500 °C, 490 °C, 480 °C, 470 °C, 460 °C or 450 °C, etc., preferably below 480 °C. After cooling, the components with an atmospheric distillation range above 350 °C are condensed, such as 350 °C, 360 °C, 380 °C, 400 °C, 420 °C, 450 °C, 480 °C or 500 °C, etc., to obtain recycle oil.

[0046] In the present invention, since the partial pressure of the oil and gas product is lower than atmospheric pressure, the components with an atmospheric distillation range below 500 °C can maintain a gaseous state at the above-mentioned gas phase temperature.

[0047] In the present invention, after the recycle oil yield is increased, the increase is approximately about 70% of the slurry oil production of the raw material in one-pass reaction; since the recycle oil obtained by condensing the oil and gas is cooled by a part of the recycle oil as the cooling medium, the return tower temperature and return tower flow rate of the recycle oil are adjusted according to the content of the components with an atmospheric distillation range ≤ 350 °C in the recycle oil.

[0048] As a preferred technical solution of the present invention, the fresh raw material in step (2) includes any one or at least two combinations of hydrocracking tail oil, coker wax oil, vacuum gas oil, atmospheric residue or vacuum residue. Typical but non-limiting examples of the combinations are: the combination of hydrocracking tail oil and coker wax oil, the combination of coker wax oil and vacuum gas oil, the combination of vacuum gas oil, atmospheric residue and vacuum residue, etc.

[0049] Preferably, the feeding temperature of the fresh feedstock in step (2) is 180 - 260°C, such as 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or 260°C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] Preferably, the volume ratio of the slurry to the fresh feedstock in step (2) is 1:20 - 1:50, such as 1:20, 1:25, 1:30, 1:35, 1:40, 1:45 or 1:50, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] In the present invention, after the yield of the recycle oil increases, the corresponding yield of the slurry will decrease significantly, even dropping below 30% of the original yield. It is difficult to ensure long-term operation only by using the heavy slurry to recycle heat and send it out. Therefore, the measure of feeding fresh feedstock to the bottom of the fractionating tower is adopted to dilute the slurry. The fresh feedstock is the feed of the FCC or DCC unit and does not include the recycle components.

[0052] Preferably, the bottom temperature of the fractionating tower in step (2) is 330 - 370°C, such as 330°C, 335°C, 340°C, 345°C, 350°C, 360°C or 370°C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable. Preferably, it is 330 - 350°C.

[0053] Preferably, the fresh feedstock in step (2) enters the fractionating tower in two paths. One path is mixed with the liquid phase condensed by the chevron baffle of the fractionating tower and then enters the bottom of the fractionating tower, and the other path directly enters the bottom of the fractionating tower.

[0054] Preferably, the mixed raw material obtained after mixing in step (2) is taken out as the bottom oil of the tower, and after being pressurized, it is divided into three parts, and the last part is urgently discharged externally.

[0055] In the present invention, in order to cope with emergencies, an emergency external discharge process is reserved for the bottom pump of the fractionating tower; the content of heavy slurry in the bottom oil of the tower is about 3%. Because the fresh feed dilutes the easily coking substances such as olefins in the slurry and also dilutes the catalyst powder, the coking situation at the bottom of the fractionating tower is greatly slowed down, making the bottom circulation system of the fractionating tower basically able to achieve ultra-long-term operation.

[0056] Since the oil and gas contain solid particles, mainly catalyst powder, after washing, they enter the slurry. The solid content in the slurry is generally controlled to be no more than 0.6 g / L. After using fresh raw materials to enter the fractionating tower, the solid content in the mixed raw materials can be reduced to below 0.018 g / L. The lower solid content is beneficial to the long-term operation of the unit. After using the mixed raw materials to wash the catalyst powder carried in the oil and gas, the main control index is that the solid content in the recycle oil is no more than 20 mg / L. In actual operation, the solid content in the recycle oil is generally about 2 mg / L.

[0057] Preferably, the proportion of the bottom tower oil returned to the fractionating tower in step (2) in the total amount of bottom tower oil withdrawn is 30 - 70 wt%, such as 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt% or 70 wt%, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0058] Preferably, this part of the bottom tower oil returned to the fractionating tower in step (2) is first heat-exchanged and then returned to the fractionating tower. The temperature after heat exchange is 280 - 330 °C, such as 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0059] Preferably, the bottom tower oil returned to the fractionating tower in step (2) exchanges heat with the oil and gas product at the chevron baffle and washes the catalyst powder carried in the oil and gas product.

[0060] In the present invention, the control of the bottom temperature of the fractionating tower is mainly based on the washing effect of the part of the bottom tower oil returning to the tower on the reaction oil and gas. If the solid content in the recycle oil is lower than 20 mg / L, the operation can be kept unchanged. If the solid content in the recycle oil is higher than 20 mg / L, it is necessary to appropriately increase the bottom temperature, reduce the heat extraction amount of the bottom tower oil, and further increase the washing circulation amount. When the bottom temperature is higher than 330 °C, it is beneficial to increase the washing oil volume and also beneficial to the extraction of light components, increasing the recycle oil yield.

[0061] In the present invention, the slurry in the traditional fractionation unit needs to be discharged in time. One reason is that as the fractionation process continues, the solid content in the slurry exceeds 0.6 g / L. The other reason is that the recycle ratio is increasing, which affects the processing capacity of the fresh feedstock in the reaction unit. The main reason for this is that the conversion rate of three-ring and four-ring aromatic hydrocarbons in the slurry in the reaction unit is relatively low or basically unchanged. They accumulate more and more in the unit, and due to their strong adsorption ability, the conversion rate of the fresh feedstock decreases. In the present invention, by increasing the gas-phase temperature above the chevron baffle in the fractionation tower, the content of three-ring and four-ring aromatic hydrocarbons in the oil products condensed from the high-temperature oil gas can be significantly reduced, avoiding the accumulation of three-ring and four-ring aromatic hydrocarbons in the system. In catalytic cracking or catalytic pyrolysis reactions, polycyclic aromatic hydrocarbons with five or more rings can have a relatively high conversion rate at a relatively low reaction severity, and there is no problem affecting the conversion rate with the fresh feedstock. At this time, full conversion of the heavy slurry with an atmospheric distillation range above 500 °C in the bottom oil of the tower can be achieved, and the coking rate during the catalytic cracking reaction of polycyclic aromatic hydrocarbons with five or more rings is about 50%.

[0062] As a preferred technical solution of the present invention, the recycle oil in step (3) is taken out from the tray area of the fractionation tower.

[0063] Preferably, the recycle oil is drawn from the first or second tray from the bottom up.

[0064] Preferably, the recycle oil in step (3) is a component of the oil and gas product with an atmospheric distillation range of not less than 350 °C, such as 350 °C, 360 °C, 380 °C, 400 °C, 420 °C, 450 °C, 480 °C or 500 °C, etc. When the aromatic hydrocarbon content in the recycle oil is less than 40%, 20 - 50 wt% of the recycle oil is returned to the reaction unit for recycling, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt% or 50 wt%, etc. When the aromatic hydrocarbon content in the recycle oil is not less than 40%, the recycle oil is not returned to the reaction unit for recycling.

[0065] In the present invention, the flow rate of the recycle oil returned to the reaction unit for recycling is controlled according to the aromatic hydrocarbon content of the recycle oil. When the content of three-ring and four-ring aromatic hydrocarbons in the recycle oil is less than 40%, a certain recycle flow rate of the recycle oil needs to be maintained; when the content of three-ring and four-ring aromatic hydrocarbons in the recycle oil is between 40 - 60%, it is no longer necessary to recycle, and it can be directly used as a product.

[0066] Preferably, the extraction temperature of the recycle oil in step (3) is 300 - 350 °C, such as 300 °C, 310 °C, 320 °C, 330 °C, 340 °C or 350 °C, etc., but not limited to the listed values. Other unlisted values within this numerical range are also applicable, and preferably 300 - 330 °C.

[0067] In the present invention, the temperature of the recycled oil withdrawn should not be higher than 350 °C, which is convenient for the long-term stable operation of the recycled oil unit; the temperature of the recycled oil withdrawn can be achieved by adjusting the temperature and flow rate of the recycled oil returning to the tower, and it is preferably not lower than 300 °C to avoid the recycled oil carrying too many components with an atmospheric distillation range ≤ 350 °C.

[0068] As a preferred technical solution of the present invention, in step (3), except for the part of the recycled oil used for reaction recycling, the other part of the recycled oil is divided into two parts after heat exchange and cooling, and the temperature after heat exchange and cooling is 180 - 250 °C, such as 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C or 250 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0069] Preferably, the recycled oil taken out as the raw material for making needle coke is further cooled by heat exchange to 70 - 90 °C and taken out, such as 70 °C, 75 °C, 80 °C, 85 °C or 90 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0070] Preferably, the recycled oil returned to the fractionating tower accounts for 30 - 70 wt% of the total amount of recycled oil, such as 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 60 wt% or 70 wt%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable; the recycled oil taken out as the raw material for making needle coke accounts for 10 - 20 wt%, such as 10 wt%, 12 wt%, 15 wt%, 18 wt% or 20 wt%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0071] Preferably, the recycled oil returned to the separation tower is added from the 4th or 5th tray.

[0072] Preferably, when the recycled oil is taken out from the 2nd tray, a part of the recycled oil returned to the fractionating tower that has not been cooled by heat exchange is returned from the 1st tray.

[0073] Preferably, the recycled oil returned to the 1st tray accounts for 10 - 30 wt% of the total amount of the recycled oil returned to the fractionating tower, such as 10 wt%, 15 wt%, 20 wt%, 25 wt% or 30 wt%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0074] In the present invention, the recycle oil is withdrawn from the first or second tray, and a gas-lifting draw-off bucket is arranged on the draw-off tray to facilitate the collection of all the cooled recycle oil components, so as to improve the recycle oil yield. When the draw-off bucket is arranged on the second tray, a hot recycle oil return line needs to be arranged at the outlet of the recycle oil transfer pump to return to the first tray; when the recycle oil draw-off bucket is arranged on the first tray, the hot recycle oil return line does not need to be arranged.

[0075] In a third aspect, the present invention provides a use of the above fractionation device, and the recycle oil withdrawn from the fractionation device is used as a raw material for producing needle coke.

[0076] Preferably, the recycle oil withdrawn from the fractionation device is also used for producing oil-based carbon fiber and / or for blending marine fuel oil.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] (1) By improving the fractionation device and process, the present invention increases the gas phase temperature above the chevron baffle of the fractionation tower, enabling the components suitable for preparing needle coke to enter the recycle oil, thus solving the problems of ash content and carbon residue existing in the traditional process using slurry as raw material from the source. No pretreatment is required, which helps simplify the device and process and reduce production costs.

[0079] (2) After the components suitable for preparing needle coke enter the recycle oil in the present invention, solid particles and carbon residue still remain in the slurry and basically do not enter the recycle oil. The solid content of the recycle oil can be controlled within 10 mg / L, the ash content is reduced to about 2 mg / L, and the carbon residue content is reduced to within 4 wt%, reducing the difficulty of subsequent utilization of the recycle oil and meeting the requirements of raw materials for needle coke, petroleum carbon fiber, and marine fuel oil blending.

[0080] (3) The present invention uses fresh raw materials to dilute the slurry, dispersing the olefins and other substances prone to coking in the slurry and significantly reducing the content of catalyst powder, effectively avoiding the problem of easy coking at the bottom of the fractionation tower, ensuring the long-term stable operation of the fractionation tower, and realizing the full recycling of heavy slurry.

[0081] (4) The fractionation device of the present invention has few structural changes, but remarkable improvement effects, low cost, and wide application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 FIG. is a schematic structural diagram of a fractionation device in a catalytic cracking process provided by Embodiment 1 of the present invention;

[0083] Figure 2 FIG. is a schematic structural diagram of a fractionation device in a catalytic cracking process provided by Comparative Example 1 of the present invention;

[0084] Among them, 1 - fractionating tower, 11 - chevron baffle, 12 - tray, 21 - reaction oil and gas feed pipeline, 22 - fresh feedstock feed pipeline, 30 - bottom oil transfer pump of the tower, 31 - first branch pipeline of the bottom oil of the tower, 32 - second branch pipeline of the bottom oil of the tower, 33 - third branch pipeline of the bottom oil of the tower, 34 - bottom oil heat exchanger, 341 - first heat exchanger of the bottom oil of the tower, 342 - second heat exchanger of the bottom oil of the tower, 35 - bottom oil quench pipeline, 36 - bottom oil washing pipeline, 40 - recycle oil storage equipment, 41 - first branch pipeline of the recycle oil, 42 - cold reflux pipeline of the second branch of the recycle oil, 42' - hot reflux pipeline of the second branch of the recycle oil, 43 - third branch pipeline of the recycle oil, 44 - recycle oil transfer pump, 45 - recycle oil heat exchanger, 5 - filter, 6 - external slurry pump, 7 - external slurry cooler. Detailed implementation manners

[0085] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0086] The following are typical but non - restrictive embodiments of the present invention:

[0087] Embodiment 1:

[0088] This embodiment provides a fractionation device in the catalytic cracking process. The structural schematic diagram of the fractionation device is as Figure 1 shown, including a fractionating tower 1, a feed unit, a bottom oil unit, and a recycle oil unit. The feed unit is connected to the lower inlet of the fractionating tower 1. The bottom outlet of the fractionating tower 1 is connected to the bottom oil unit, and the middle outlet of the fractionating tower 1 is connected to the recycle oil unit;

[0089] The feed unit includes a reaction oil and gas feed pipeline 21 and a fresh feedstock feed pipeline 22. The bottom oil unit includes a first branch pipeline 31 of the bottom oil of the tower and a second branch pipeline 32 of the bottom oil of the tower. The first branch pipeline 31 of the bottom oil of the tower is connected to the catalytic cracking device, and the second branch pipeline 32 of the bottom oil of the tower is connected to the bottom oil reflux port of the fractionating tower 1. The recycle oil unit includes a recycle oil storage equipment 40, a first branch pipeline 41 of the recycle oil, a second branch pipeline of the recycle oil, and a third branch pipeline 43 of the recycle oil. Among the branch pipelines separated from the recycle oil storage equipment 40, the first branch pipeline 41 of the recycle oil is connected to the catalytic cracking device, the second branch pipeline of the recycle oil is connected to the recycle oil reflux port of the fractionating tower 1, and the third branch pipeline 43 of the recycle oil is a pipeline for extracting raw materials for making needle - shaped coke.

[0090] Inside the fractionating tower 1, a chevron baffle 11 is provided at the lower part, and trays 12 are provided in the middle and upper parts.

[0091] The number of trays 12 is 30. The tray for withdrawing recycled oil is the second tray, and a gas-lifting withdrawal hopper is provided thereon.

[0092] The reaction oil-gas feed pipeline 21 in the feed unit is connected to the inlet of the fractionating tower 1, which is located below the chevron baffle 11.

[0093] The fresh feedstock feed pipeline 22 is divided into two branches. One branch is connected to the bottom of the fractionating tower 1, and the other branch is connected above the bottom of the fractionating tower 1. Its inlet is located below the inlet of the reaction oil-gas feed pipeline 21.

[0094] The bottoms unit further includes a bottoms transfer pump 30. The bottom outlet of the fractionating tower 1 is connected to the inlet of the bottoms transfer pump 30, and the outlet of the bottoms transfer pump 30 is connected to a bottoms branch pipeline.

[0095] A bottoms heat exchanger 34 is provided on the second bottoms branch pipeline 32; the bottoms heat exchanger 34 is a cooler, and a steam generator is specifically selected.

[0096] The bottoms reflux port connected by the second bottoms branch pipeline 32 is located between the chevron baffle 11 and the trays 12.

[0097] The bottoms unit further includes a third bottoms branch pipeline 33, and the third branch pipeline 33 is connected to the emergency blowdown unit.

[0098] The middle outlet of the fractionating tower 1 is connected to the recycled oil storage device 40 through a recycled oil withdrawal pipeline.

[0099] The recycled oil unit further includes a recycled oil transfer pump 44. The outlet of the recycled oil storage device 40 is connected to the inlet of the recycled oil transfer pump 44, and the outlet of the recycled oil transfer pump 44 is connected to a recycled oil branch pipeline.

[0100] A recycled oil heat exchanger 45 is provided in the recycled oil branch pipeline. The first recycled oil branch pipeline 41 does not pass through the recycled oil heat exchanger 45, and the third recycled oil branch pipeline 43 passes through the recycled oil heat exchanger 45.

[0101] The second recycled oil branch pipeline is further divided into two branches. One branch passes through the recycled oil heat exchanger 45 and is the cold reflux pipeline 42 of the second recycled oil branch. The other branch does not pass through the recycled oil heat exchanger 45 and is the hot reflux pipeline 42' of the second recycled oil branch. The branch pipeline passing through the recycled oil heat exchanger 45 is connected to the cold reflux port of the recycled oil in the fractionating tower 1, and the branch pipeline not passing through the recycled oil heat exchanger 45 is connected to the hot reflux port of the recycled oil in the fractionating tower 1.

[0102] A raw material heat exchanger for making needle coke is further provided on the third recycled oil branch pipeline 43.

[0103] Example 2:

[0104] This example provides a fractionation device in the catalytic cracking process. The fractionation device includes a fractionating tower 1, a feed unit, a bottom oil unit, and a recycle oil unit. The feed unit is connected to the lower inlet of the fractionating tower 1. The bottom outlet of the fractionating tower 1 is connected to the bottom oil unit, and the middle outlet of the fractionating tower 1 is connected to the recycle oil unit.

[0105] The feed unit includes a reaction oil and gas feed pipeline 21 and a fresh feed pipeline 22. The bottom oil unit includes a first branch pipeline 31 of the bottom oil and a second branch pipeline 32 of the bottom oil. The first branch pipeline 31 of the bottom oil is connected to the catalytic cracking device, and the second branch pipeline 32 of the bottom oil is connected to the bottom oil reflux port of the fractionating tower 1. The recycle oil unit includes a recycle oil storage device 40, a first branch pipeline 41 of the recycle oil, a second branch pipeline of the recycle oil, and a third branch pipeline 43 of the recycle oil. Among the branch pipelines branched from the recycle oil storage device 40, the first branch pipeline 41 of the recycle oil is connected to the catalytic cracking device, the second branch pipeline of the recycle oil is connected to the recycle oil reflux port of the fractionating tower 1, and the third branch pipeline 43 of the recycle oil is a pipeline for extracting raw materials for making needle coke.

[0106] An inverted valve tray 11 is provided in the lower part of the fractionating tower 1, and trays 12 are provided in the upper and middle parts.

[0107] The number of trays 12 is 27. The tray for extracting recycle oil is the first tray, and a lifting gas extraction hopper is provided thereon.

[0108] The reaction oil and gas feed pipeline 21 in the feed unit is connected to the inlet of the fractionating tower 1, which is located below the inverted valve tray 11.

[0109] The reaction oil and gas feed pipeline 21 in the feed unit is connected to the inlet of the fractionating tower 1, which is located below the inverted valve tray 11.

[0110] The fresh feed pipeline 22 is divided into two branches. One branch is connected to the bottom of the fractionating tower 1, and the other branch is connected above the bottom of the fractionating tower 1. Its inlet is located below the inlet of the reaction oil and gas feed pipeline 21.

[0111] The bottom oil unit further includes a bottom oil transfer pump 30. The bottom outlet of the fractionating tower 1 is connected to the inlet of the bottom oil transfer pump 30, and the outlet of the bottom oil transfer pump 30 is connected to the bottom oil branch pipeline.

[0112] A bottom oil heat exchanger 34 is provided on the second branch pipeline 32 of the bottom oil. The bottom oil heat exchanger 34 is a shell-and-tube heat exchanger.

[0113] The bottom oil reflux port connected by the second branch pipeline 32 of the bottom oil is located between the inverted valve tray 11 and the trays 12.

[0114] The bottom tower oil unit further includes a third branch pipeline 33 of the bottom tower oil, and the third branch pipeline 33 is connected to the emergency external discharge unit.

[0115] The middle outlet of the fractionating tower 1 is connected to the recycle oil storage device 40 through a recycle oil extraction pipeline.

[0116] The recycle oil unit further includes a recycle oil transfer pump 44. The outlet of the recycle oil storage device 40 is connected to the inlet of the recycle oil transfer pump 44, and the outlet of the recycle oil transfer pump 44 is connected to a recycle oil branch pipeline.

[0117] A recycle oil heat exchanger 45 is provided in the recycle oil branch pipeline. The first recycle oil branch pipeline 41 does not pass through the recycle oil heat exchanger 45, and the third recycle oil branch pipeline 43 passes through the recycle oil heat exchanger 45.

[0118] The second recycle oil branch pipeline passes through the recycle oil heat exchanger 45 to be a cold reflux pipeline 42 of the second recycle oil branch, and is connected to the cold reflux port of the recycle oil of the fractionating tower 1.

[0119] A raw material heat exchanger for making needle coke is further provided on the third recycle oil branch pipeline 43.

[0120] Example 3:

[0121] This embodiment provides a fractionation method in the catalytic cracking process. The fractionation method is carried out by using the fractionation device in Example 1 and includes the following steps:

[0122] (1) Fractionate the oil-gas product after the fluid catalytic cracking reaction in the fractionating tower 1. The oil-gas product sequentially passes through the herringbone baffle area and the tray area in the fractionating tower 1. The liquid phase condensed in the herringbone baffle area enters the tower bottom to form slurry. The gas phase temperature after passing through the herringbone baffle area is 380 °C. The components in the oil-gas product with an atmospheric distillation range below 480 °C remain in the gas phase and rise to the tray area of the fractionating tower 1. After cooling, the components with an atmospheric distillation range of 360-480 °C are condensed to obtain recycle oil;

[0123] (2) Mix the slurry obtained in step (1) with fresh feedstock. The fresh feedstock is hydrocracked tail oil, and the feed temperature is 220°C. The volume ratio of the slurry to the fresh feedstock is 1:50. The fresh feedstock enters the fractionating tower 1 in two streams. One stream is mixed with the liquid phase condensed by the chevron baffle 11 in the fractionating tower 1 and then enters the bottom of the fractionating tower 1. The other stream is directly introduced into the bottom of the fractionating tower 1. The bottom temperature of the fractionating tower 1 is 350°C. The mixed feedstock obtained after mixing is taken out as the bottom oil of the tower. After being pressurized, it is divided into two parts. One part is used as the feed for the fluid catalytic cracking unit, and the other part is first heat-exchanged. The temperature after heat exchange is 280°C, and then it returns to the fractionating tower 1 to exchange heat with the oil-gas product in step (1) and wash the catalyst powder carried in the oil-gas product. The proportion of the bottom oil returning to the fractionating tower 1 in the total amount of the bottom oil taken out of the tower is 70 wt%, and at the same time, the taken-out bottom oil is also connected with an emergency external discharge process;

[0124] (3) The recycle oil obtained in step (1) is taken out from the second tray of the fractionating tower 1 and divided into three parts. The extraction temperature of the recycle oil is 320°C. 20 wt% of the recycle oil returns to the fluid catalytic cracking unit for reaction and recycling. 60 wt% of the recycle oil returns to the fractionating tower 1. This part is further divided into two parts. 40 wt% of the recycle oil is heat-exchanged and cooled to a temperature of 220°C and added from the fourth tray as a cooling medium for condensing the oil-gas product. 20 wt% of the recycle oil is added from the first tray without heat-exchanging and cooling. The last part of the recycle oil is heat-exchanged and cooled to a temperature of 80°C and then taken out as the raw material for making needle coke.

[0125] In this embodiment, by fractionating the oil-gas product using the above method, the content of components in the recycle oil with a boiling range of 360 - 480°C reaches more than 90%, the solid content in the recycle oil is 6 mg / L, the total amount of three-ring and four-ring aromatics in the recycle oil reaches 45 wt%, and the carbon residue content is 1.6 wt%.

[0126] Example 4:

[0127] This embodiment provides a fractionation method in the fluid catalytic cracking process. The fractionation method is carried out using the fractionation device in Example 1 and includes the following steps:

[0128] (1) Fractionate the oil-gas product after the fluid catalytic cracking reaction in the fractionating tower 1. The oil-gas product passes through the chevron baffle area and the tray area in the fractionating tower 1 in sequence. The liquid phase condensed in the chevron baffle area enters the bottom of the tower to form slurry. The temperature of the gas phase after passing through the chevron baffle area is 400°C. The components in the oil-gas product with an atmospheric distillation range below 500°C remain in the gas phase and rise to the tray area of the fractionating tower 1. After being cooled, the components with an atmospheric distillation range of 360 - 500°C are condensed to obtain recycle oil;

[0129] (2) Mix the slurry oil obtained in step (1) with fresh feedstock. The fresh feedstock is vacuum residue, and the feed temperature is 200 °C. The volume ratio of the slurry oil to the fresh feedstock is 1:30. The fresh feedstock enters the fractionating tower 1 in two streams. One stream is mixed with the liquid phase condensed by the chevron baffle 11 in the fractionating tower 1 and then enters the bottom of the fractionating tower 1. The other stream is directly introduced into the bottom of the fractionating tower 1. The bottom temperature of the fractionating tower 1 is 360 °C. The mixed feedstock obtained after mixing is taken out as the bottom oil of the tower. After pressurization, it is divided into two parts. One part is used as the feedstock for the fluid catalytic cracking unit. The other part is first heat-exchanged, and the temperature after heat exchange is 290 °C. Then it returns to the fractionating tower 1 to exchange heat with the oil-gas product in step (1) and wash the catalyst powder carried in the oil-gas product. The proportion of the bottom oil returning to the fractionating tower 1 in the total amount of the bottom oil taken out of the tower is 60 wt%.

[0130] (3) The recycle oil obtained in step (1) is taken out from the second tray of the fractionating tower 1 and divided into three parts. The extraction temperature of the recycle oil is 325 °C. 30 wt% of the recycle oil returns to the fluid catalytic cracking unit for reaction and recycling. 50 wt% of the recycle oil returns to the fractionating tower 1. This part is further divided into two parts. 30 wt% of the recycle oil is cooled by heat exchange to a temperature of 230 °C and added from the fifth tray as a cooling medium to condense the oil-gas product. 20 wt% of the recycle oil is added from the first tray without heat exchange cooling. The last part of the recycle oil is cooled by heat exchange to a temperature of 75 °C and then taken out as the raw material for making needle coke.

[0131] In this example, by fractionating the oil-gas product using the above method, the content of components in the recycle oil with a temperature range of 360 - 500 °C reaches more than 90%, the solid content in the recycle oil is 5 mg / L, the total amount of three-ring and four-ring aromatics in the recycle oil reaches 50 wt%, and the carbon residue content is 2.1 wt%.

[0132] Example 5:

[0133] This example provides a fractionation method during catalytic cracking. The fractionation method is carried out using the fractionation device in Example 2 and includes the following steps:

[0134] (1) Fractionate the oil-gas product after catalytic cracking in the fractionating tower 1. The oil-gas product successively passes through the chevron baffle area and the tray area in the fractionating tower 1. The liquid phase condensed in the chevron baffle area enters the bottom of the tower to form slurry oil. The temperature of the gas phase after passing through the chevron baffle area is 380 °C. The components in the oil-gas product with an atmospheric distillation range below 480 °C remain in the gas phase and rise to the tray area of the fractionating tower 1. After cooling, the components with an atmospheric distillation range of 360 - 480 °C are condensed to obtain recycle oil.

[0135] (2) Mix the slurry oil obtained in step (1) with fresh feedstock. The fresh feedstock is coker gas oil and vacuum gas oil with a volume ratio of 1:1, and the feed temperature is 260°C. The volume ratio of the slurry oil to the fresh feedstock is 1:40. The fresh feedstock enters the fractionating tower 1 in two paths. One path mixes with the liquid phase condensed by the chevron baffle 11 in the fractionating tower 1 and then enters the bottom of the fractionating tower 1. The other path directly enters the bottom of the fractionating tower 1. The bottom temperature of the fractionating tower 1 is 340°C. The mixed raw material obtained after mixing is taken out as the bottom oil of the tower. After pressurization, it is divided into two parts. One part is used as the feed for the catalytic cracking unit, and the other part is first heat-exchanged. The temperature after heat exchange is 300°C, and then it returns to the fractionating tower 1 to exchange heat with the oil-gas product in step (1) and wash the catalyst powder carried in the oil-gas product. The proportion of the bottom oil returning to the fractionating tower 1 in the total amount of the bottom oil taken out of the tower is 50 wt%, and at the same time, the taken-out bottom oil is also connected with an emergency external discharge process;

[0136] (3) Take out the recycle oil obtained in step (1) from the first tray of the fractionating tower 1 and divide it into three parts. The extraction temperature of the recycle oil is 320°C. 35 wt% of the recycle oil returns to the catalytic cracking unit for reaction and recycling. 55 wt% of the recycle oil is cooled by heat exchange to a temperature of 210°C and then returns to the fractionating tower 1 as a cooling medium and is added from the fourth tray to condense the oil-gas product. The last part of the recycle oil is cooled by heat exchange to a temperature of 90°C and then taken out as the raw material for making needle coke.

[0137] In this example, by fractionating the oil-gas product using the above method, the content of components in the recycle oil with a temperature range of 360 - 480°C reaches more than 95%, the solid content in the recycle oil is 5 mg / L, the total amount of three-ring and four-ring aromatic hydrocarbons in the recycle oil reaches 50 wt%, and the carbon residue content is 2.5 wt%.

[0138] Example 6:

[0139] This example provides a fractionation method during catalytic cracking. The fractionation method is carried out using the fractionation device in Example 2 and includes the following steps:

[0140] (1) Fractionate the oil-gas product after catalytic cracking in the fractionating tower 1. The oil-gas product passes through the chevron baffle area and the tray area in the fractionating tower 1 in sequence. The liquid phase condensed in the chevron baffle area enters the bottom of the tower to form slurry oil. The temperature of the gas phase after passing through the chevron baffle area is 360°C. The components in the oil-gas product with an atmospheric distillation range below 500°C remain in the gas phase and rise to the tray area of the fractionating tower 1. After cooling, the components with an atmospheric distillation range of 360 - 500°C are condensed to obtain recycle oil;

[0141] (2) Mix the slurry oil obtained in step (1) with fresh feedstock. The fresh feedstock is atmospheric residue oil, and the feed temperature is 240 °C. The volume ratio of the slurry oil to the fresh feedstock is 1:25. The fresh feedstock enters the fractionating tower 1 in two streams. One stream is mixed with the liquid phase condensed by the chevron baffle 11 of the fractionating tower 1 and then enters the bottom of the fractionating tower 1. The other stream is directly introduced into the bottom of the fractionating tower 1. The bottom temperature of the fractionating tower 1 is 360 °C. The mixed feedstock obtained after mixing is taken out as the bottom oil of the tower. After pressurization, it is divided into two parts. One part is used as the feed for the catalytic cracking unit, and the other part is first heat-exchanged. The temperature after heat exchange is 310 °C, and then it returns to the fractionating tower 1 to exchange heat with the oil and gas products in step (1) and wash the catalyst powder carried in the oil and gas products. The proportion of the bottom oil of the tower returning to the fractionating tower 1 in the total amount of the bottom oil of the tower taken out is 65 wt%.

[0142] (3) The recycle oil obtained in step (1) is taken out from the first tray of the fractionating tower 1 and divided into three parts. The extraction temperature of the recycle oil is 325 °C. 40 wt% of the recycle oil returns to the catalytic cracking unit for reaction and recycling. 45 wt% of the recycle oil is cooled by heat exchange to a temperature of 240 °C and returns to the fractionating tower 1 as a cooling medium and is added from the fourth tray to condense the oil and gas products. The last part of the recycle oil is cooled by heat exchange to a temperature of 85 °C and then taken out as the raw material for producing oil-based carbon fiber.

[0143] In this example, the oil and gas products are fractionated by the above method. The content of components in the recycle oil at 360 - 500 °C reaches more than 90%, the solid content in the recycle oil is 4 mg / L, the total amount of three-ring and four-ring aromatic hydrocarbons in the recycle oil reaches 52 wt%, and the carbon residue content is 3.5 wt%.

[0144] Comparative Example 1:

[0145] This comparative example provides a fractionating device in the catalytic cracking process. The structural schematic diagram of the fractionating device is as Figure 2 shown, including a fractionating tower 1, a feed unit, and a bottom oil unit. The feed unit is connected to the lower inlet of the fractionating tower 1, and the bottom outlet of the fractionating tower 1 is connected to the bottom oil unit;

[0146] The feed unit includes a reaction oil and gas feed pipeline 21; the bottom oil unit includes a first branch pipeline 31 of the bottom oil, a bottom oil quench pipeline 35, and a bottom oil washing pipeline 36. The first branch pipeline 31 of the bottom oil is connected to the catalytic cracking unit. The bottom oil quench pipeline 35 is connected to the bottom reflux port of the fractionating tower 1. The bottom oil washing pipeline 36 is connected to the washing reflux port above the chevron baffle of the fractionating tower 1;

[0147] The bottom oil unit further includes a bottom oil transfer pump 30. A filter 5 is provided between the bottom outlet of the fractionating tower 1 and the bottom oil transfer pump 30.

[0148] On the connecting pipeline of the bottom tower oil transfer pump 30 with the bottom tower oil quench pipeline 35 and the bottom tower oil washing pipeline 36, a first bottom tower oil heat exchanger 341 and a second bottom tower oil heat exchanger 342 are successively arranged, and then it is divided into two pipelines, namely the bottom tower oil quench pipeline 35 and the bottom tower oil washing pipeline 36. Among them, a circulation pipeline is directly arranged after passing through the first bottom tower oil heat exchanger 341 and connected to the bottom tower oil washing pipeline 36.

[0149] The first bottom tower oil heat exchanger 341 is a conventional heat exchanger, and the second bottom tower oil heat exchanger 342 is a steam generator.

[0150] After the first bottom tower oil heat exchanger 341 and the second bottom tower oil heat exchanger 342, there is also an external oil slurry pipeline, and an external oil slurry pump 6 and an external oil slurry cooler 7 are arranged on the external oil slurry pipeline.

[0151] Comparative Example 2:

[0152] This comparative example provides a fractionation method in the catalytic cracking process. The method is carried out using the fractionation device in Comparative Example 1. The method adopts the traditional fractionation method without increasing the gas phase temperature above the chevron baffle. The components below 480 °C are condensed and enter the oil slurry, and the oil slurry is still used as the raw material for producing needle coke.

[0153] In this comparative example, when fractionating the oil and gas products by the above method, the solid content of the oil slurry is 3000 mg / L, the carbon residue content is 7.5 wt%, and the total amount of tricyclic and tetracyclic aromatic hydrocarbons reaches 47 wt%. After the oil slurry is sent out, it needs to be further treated for solid removal and carbon residue removal to meet the requirements of the needle coke raw material.

[0154] From the above-mentioned examples and comparative examples, it can be seen that the present invention improves the gas phase temperature above the chevron baffle of the fractionation tower by improving the fractionation device and process, so that the components rich in tricyclic and tetracyclic aromatic hydrocarbons suitable for preparing needle coke enter the recycle oil, solving the problems of ash and carbon residue existing in the traditional method using oil slurry as the raw material from the source, without the need for pretreatment, which helps to simplify the device and process and reduce the production cost; after the components suitable for preparing needle coke in the present invention enter the recycle oil, the solid particles and carbon residue still remain in the oil slurry and basically do not enter the recycle oil. The solid content of the recycle oil can be controlled within 10 mg / L, the ash content is reduced to about 2 mg / L, and the carbon residue content is reduced to within 4 wt%, reducing the difficulty of subsequent utilization of the recycle oil and meeting the requirements of the raw materials for needle coke, petroleum carbon fiber, and marine fuel oil blending; the present invention uses fresh raw materials to dilute the oil slurry, so that the olefins and other substances prone to coking in the oil slurry are dispersed, and the content of catalyst powder is greatly reduced, effectively avoiding the problem of easy coking at the bottom of the fractionation tower, ensuring the long-term stable operation of the fractionation tower, and realizing the full recycle of heavy oil slurry; the structure of the fractionation device is changed less, but the improvement effect is remarkable, the cost is low, and the applicable range is wide.

[0155] The applicant declares that the present invention illustrates the detailed apparatus and method of the present invention through the above embodiments, but the present invention is not limited to the above detailed apparatus and method, that is, it does not mean that the present invention must rely on the above detailed apparatus and method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the apparatus of the present invention, the addition of auxiliary devices, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A fractionation unit in a catalytic cracking or catalytic pyrolysis process, characterized in that, The fractionation unit includes a fractionating tower, a feed unit, a bottom oil unit, and a recycle oil unit. The feed unit is connected to the lower inlet of the fractionating tower. The bottom outlet of the fractionating tower is connected to the bottom oil unit, and the middle outlet of the fractionating tower is connected to the recycle oil unit. The feed unit includes a reaction oil and gas feed pipeline and a fresh feed pipeline. The bottom oil unit includes a first bottom oil branch pipeline and a second bottom oil branch pipeline. The first bottom oil branch pipeline is connected to a fluid catalytic cracking unit or a catalytic pyrolysis unit, and the second bottom oil branch pipeline is connected to the bottom oil reflux port of the fractionating tower. The recycle oil unit includes a recycle oil storage device, a first recycle oil branch pipeline, a second recycle oil branch pipeline, and a third recycle oil branch pipeline. Among the branch pipelines separated from the recycle oil storage device, the first recycle oil branch pipeline is connected to a fluid catalytic cracking unit or a catalytic pyrolysis unit, the second recycle oil branch pipeline is connected to the recycle oil reflux port of the fractionating tower, and the third recycle oil branch pipeline is a pipeline for extracting raw materials for making needle coke. A chevron baffle is provided in the lower part inside the fractionating tower, and trays are provided in the middle and upper parts. The fresh feed pipeline is divided into two branches. One branch is connected to the bottom of the fractionating tower, and the other branch is connected above the bottom of the fractionating tower. Its inlet is located below the inlet of the reaction oil and gas feed pipeline. The bottom oil reflux port connected by the second bottom oil branch pipeline is located between the chevron baffle and the trays.

2. The fractionation device according to claim 1, characterized in that, The number of trays in the fractionating tower is 26 - 32 layers.

3. The fractionation device according to claim 1, characterized in that, A gas-lifting extraction hopper is provided on the tray for extracting recycle oil.

4. The fractionation device according to claim 1, characterized in that, The connection of the reaction oil and gas feed pipeline in the feed unit to the inlet of the fractionating tower is located below the chevron baffle.

5. The fractionation device according to claim 1, wherein, The bottom oil unit further includes a bottom oil transfer pump. The bottom outlet of the fractionating tower is connected to the inlet of the bottom oil transfer pump, and the outlet of the bottom oil transfer pump is connected to the first bottom oil branch pipeline and the second bottom oil branch pipeline.

6. The fractionation device according to claim 1, characterized in that, A bottom oil heat exchanger is provided on the second bottom oil branch pipeline.

7. The fractionation device according to claim 6, characterized in that, The bottom oil heat exchanger is a cooler.

8. The fractionation device according to claim 1, characterized in that, The bottom oil unit further includes a third bottom oil branch pipeline, and the third branch pipeline is connected to an emergency external discharge unit.

9. The fractionation device according to claim 1, characterized in that, The middle outlet of the fractionating tower is connected to the recycle oil storage device through a recycle oil extraction pipeline.

10. The fractionation device according to claim 1, characterized in that, The recycle oil unit further includes a recycle oil transfer pump. The outlet of the recycle oil storage device is connected to the inlet of the recycle oil transfer pump, and the outlet of the recycle oil transfer pump is connected to the first recycle oil branch pipeline, the second recycle oil branch pipeline, and the third recycle oil branch pipeline.

11. The fractionation device according to claim 10, characterized in that, A recycle oil heat exchanger is provided in the recycle oil branch pipeline. The first recycle oil branch pipeline does not pass through the recycle oil heat exchanger, and the third recycle oil branch pipeline passes through the recycle oil heat exchanger.

12. The fractionation device according to claim 1, characterized in that, The second recycle oil branch pipeline is further divided into two branches. One branch passes through the recycle oil heat exchanger, and the other branch does not pass through the recycle oil heat exchanger. The branch pipeline passing through the recycle oil heat exchanger is connected to the cold recycle oil reflux port of the fractionating tower, and the branch pipeline not passing through the recycle oil heat exchanger is connected to the hot recycle oil reflux port of the fractionating tower.

13. The fractionation device according to claim 1, characterized in that, A raw material heat exchanger for making needle coke is further provided on the third recycle oil branch pipeline.

14. A fractionation method in a catalytic cracking or catalytic pyrolysis process, characterized in that, The fractionation method is carried out using the fractionation unit according to any one of claims 1 - 13, and includes the following steps: (1) Fractionate the oil and gas products after catalytic cracking reaction or catalytic pyrolysis reaction in a fractionating tower to obtain slurry oil and recycle oil; (2) Mix the slurry oil obtained in step (1) with fresh feedstock and divide it into at least two parts. One part is used as the feedstock for the catalytic cracking unit or catalytic pyrolysis unit, and the other part is returned to the fractionating tower to exchange heat and wash with the oil and gas products in step (1); (3) After the recycle oil obtained in step (1) is withdrawn, divide it into three parts. One part is returned to the catalytic cracking unit or catalytic pyrolysis unit for reaction and recycling, another part is returned to the fractionating tower as a cooling medium to condense the oil and gas products, and the last part is withdrawn as the raw material for making needle coke.

15. The fractionation method according to claim 14, wherein, The catalytic cracking reaction is carried out in a catalytic cracking unit.

16. The fractionation method according to claim 15, characterized in that, The catalytic cracking unit is a fluid catalytic cracking unit.

17. The fractionation method according to claim 14, wherein The catalytic pyrolysis reaction is carried out in a catalytic pyrolysis unit.

18. The fractionation method according to claim 14, characterized in that, The composition of the oil and gas products in step (1) includes dry gas, liquefied gas, gasoline, diesel oil, recycle oil and slurry oil.

19. The fractionation method according to claim 14, wherein, The oil and gas products in step (1) pass through the chevron baffle area and the tray area in the fractionating tower in sequence.

20. The fractionation method according to claim 19, characterized in that, The liquid phase condensed in the chevron baffle area enters the bottom of the tower to form slurry oil.

21. The fractionation method according to claim 19, characterized in that, The gas phase temperature after passing through the chevron baffle area is 300 - 420 °C.

22. The fractionation method according to claim 21, characterized in that, The gas phase temperature after passing through the chevron baffle area is 340 - 400 °C.

23. The fractionation method according to claim 14, wherein The components with an atmospheric distillation range below 500 °C in the oil and gas products in step (1) remain in the gas phase and rise to the tray area of the fractionating tower. After cooling, the components with an atmospheric distillation range above 350 °C are condensed to obtain recycle oil.

24. The fractionation method according to claim 14, characterized in that, The fresh feedstock in step (2) includes any one or at least two combinations of hydrocracking tail oil, coker wax oil, vacuum gas oil, atmospheric residue or vacuum residue.

25. The fractionation method according to claim 14, wherein The feed temperature of the fresh feedstock in step (2) is 180 - 260 °C.

26. The fractionation method according to claim 14, wherein, The volume ratio of the slurry oil to the fresh feedstock in step (2) is 1:20 - 1:

50.

27. The fractionation method according to claim 14, characterized in that, The bottom temperature of the fractionating tower in step (2) is 330 - 370 °C.

28. The fractionation method according to claim 27, characterized in that, The bottom temperature of the fractionating tower in step (2) is 330 - 350 °C.

29. The fractionation method according to claim 14, wherein The fresh feedstock in step (2) enters the fractionating tower in two paths. One path is mixed with the liquid phase condensed by the chevron baffle of the fractionating tower and then enters the bottom of the fractionating tower, and the other path is directly introduced into the bottom of the fractionating tower.

30. The fractionation method according to claim 14, wherein The mixed raw material obtained after mixing in step (2) is withdrawn as the bottom oil of the tower, and after pressurization, it is divided into three parts, and the last part is urgently discharged externally.

31. The fractionation method according to claim 14, characterized in that, The proportion of the bottom oil of the tower returned to the fractionating tower in step (2) in the total amount of the bottom oil of the tower withdrawn is 30 - 70 wt%.

32. The fractionation method according to claim 14, characterized in that, This part of the bottom oil of the tower returned to the fractionating tower in step (2) is first heat-exchanged and then returned to the fractionating tower, and the temperature after heat exchange is 280 - 330 °C.

33. The fractionation method according to claim 14, wherein, The bottom oil of the tower returned to the fractionating tower in step (2) exchanges heat with the oil and gas products at the chevron baffle and washes the catalyst powder carried in the oil and gas products.

34. The fractionation method according to claim 14, wherein The recycle oil in step (3) is withdrawn from the tray area of the fractionating tower.

35. The fractionation method according to claim 14, wherein, The recycle oil is withdrawn from the 1st or 2nd tray from the bottom upwards.

36. The fractionation method according to claim 14, characterized in that, The recycle oil described in step (3) is a component of the oil and gas product with an atmospheric distillation range of not less than 350 °C. When the aromatic hydrocarbon content in the recycle oil is less than 40%, 20-50 wt% of the recycle oil is returned to the reaction unit for recycling. When the aromatic hydrocarbon content in the recycle oil is not less than 40%, the recycle oil is not returned to the reaction unit for recycling.

37. The fractionation method according to claim 14, characterized in that, The extraction temperature of the recycle oil described in step (3) is 300-350 °C.

38. The fractional distillation method according to claim 37, characterized in that, The extraction temperature of the recycle oil described in step (3) is 300-330 °C.

39. The fractionation method according to claim 14, characterized in that, Except for the part used for reaction recycling in the recycle oil described in step (3), the other part of the recycle oil is divided into two parts after heat exchange and temperature reduction, and the temperature after heat exchange and temperature reduction is 200 °C - 250 °C.

40. The fractionation method according to claim 14, characterized in that, The recycle oil taken out as the raw material for producing needle coke is continuously cooled to 70-90 °C by heat exchange and then taken out.

41. The fractionation method according to claim 14, characterized in that, The recycle oil returned to the fractionating tower accounts for 30-70 wt% of the total recycle oil, and the recycle oil taken out as the raw material for producing needle coke accounts for 10-20 wt%.

42. The fractionation method according to claim 14, characterized in that, The recycle oil returned to the separation tower is added from the 4th or 5th tray.

43. The fractionation method according to claim 14, characterized in that, When the recycle oil is taken out from the 2nd tray, a part of the recycle oil returned to the fractionating tower that has not been cooled by heat exchange is returned from the 1st tray.

44. The fractionation method according to claim 43, wherein The recycle oil returned to the 1st tray accounts for 10-30 wt% of the total recycle oil returned to the fractionating tower.

45. Use of the fractionation device according to any one of claims 1-13, characterized in that, The recycle oil taken out from the fractionation unit is used as the raw material for producing needle coke.

46. The use according to claim 45, characterized in that, The recycle oil taken out from the fractionation unit is also used for producing oil-based carbon fiber and / or for blending marine fuel oil.

Images