CN110540860B

CN110540860B - Process and system for catalytic cracking by adopting double descending pipes

Info

Publication number: CN110540860B
Application number: CN201810524639.8A
Authority: CN
Inventors: 沙有鑫; 谢朝钢; 朱根权; 杨超; 成晓洁
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2018-05-28
Filing date: 2018-05-28
Publication date: 2021-08-06
Anticipated expiration: 2038-05-28
Also published as: CN110540860A

Abstract

The invention relates to a process and a system for catalytic cracking by adopting double descending pipes, wherein the process comprises the following steps: a. feeding the heavy raw material into the upper part of the first downer reactor (2) to contact with a first catalytic cracking catalyst from the top of the first downer reactor (2) and carrying out a first catalytic cracking reaction from top to bottom; b. feeding the light raw material into the upper part of a second downer reactor (9) to contact with a second catalytic cracking catalyst from the top of the second downer reactor (9) and carrying out a second catalytic cracking reaction from top to bottom; c. and (c) feeding the first product and the first semi-spent catalyst obtained in the step (a) and the second product and the second semi-spent catalyst obtained in the step (b) into a fluidized bed reactor (3) to contact with a third catalytic cracking catalyst and carry out a third catalytic cracking reaction to obtain a third product and a spent catalyst. The process and the system can improve the yield of the low-carbon olefin and simultaneously slow down the increase of the yield of the dry gas.

Description

Process and system for catalytic cracking by adopting double descending pipes

Technical Field

The invention relates to a process and a system for catalytic cracking by adopting double descending pipes.

Background

Small-molecule olefins such as ethylene, propylene and butylene are the most basic organic synthesis raw materials. At present, the main production process of small molecular olefins worldwide is a steam cracking process, but a high-temperature cracking furnace is easy to coke, so the process basically takes light oil as a raw material, such as natural gas, naphtha and light diesel oil, and can also take hydrocracking tail oil as a raw material. At present, the trend of crude oil heaviness and deterioration is more obvious in China, the yield of light oil such as naphtha is lower, and the contradiction between the supply and demand of raw materials of a steam cracking process and a catalytic reforming process is increasingly serious. Since the mid-eighties of the twentieth century, the petrochemical science research institute of the petrochemical corporation, has begun to research the catalytic cracking family technology for producing lower olefins from heavy oil, and has successfully developed the catalytic cracking (DCC, USP4980053 and USP5670037) technology for maximum production of propylene and the catalytic cracking (CPP, USP6210562) technology for maximum production of ethylene. So far, the two technologies mainly use a single riser reactor or a single riser reactor combined with a dense-phase fluidized bed reactor structure, and the yield of the dry gas and the coke is relatively high while the yield of the low-carbon olefin is improved.

In recent years, much attention has been paid to technologies for cracking heavy oil and producing light olefins in multiple reactors, which select different reactors for different raw materials, including an upward reactor, a downward reactor, and even different catalysts, so as to ensure that the raw materials react in a reaction environment more suitable for their own characteristics.

Chinese patent CN101074392A discloses a method for producing propylene and high-quality gasoline and diesel oil by two-stage catalytic cracking, which mainly utilizes two-stage riser catalytic process, adopts catalyst rich in shape-selective zeolite, takes heavy petroleum hydrocarbons or various animal and vegetable oils rich in hydrocarbon as raw materials, performs optimized combination of feeding modes aiming at reaction materials with different properties, controls reaction conditions suitable for different materials, and achieves the purposes of improving propylene yield, giving consideration to light oil yield and quality, and inhibiting generation of dry gas and coke. The feeding of the first section of riser is fresh heavy raw oil, and light hydrocarbon raw material can be fed into the lower part or the bottom of the first section of riser; the second section of riser is fed with gasoline and circulating oil with high olefin content, and can be fed in layers or mixed, and the lower part or the bottom of the second section of riser can be fed with other light hydrocarbon raw materials.

Chinese patent CN101045667A proposes a catalytic conversion method for improving the yield of low-carbon olefins, in which hydrocarbon oil raw materials are injected into a down-flow reactor through a raw material nozzle, and are contacted with a regenerated catalyst and an optional carbon deposition catalyst, a cracked product is separated from a spent catalyst, the cracked product is separated to obtain the low-carbon olefins, at least a part of the rest of the products are introduced into a riser reactor to be contacted with a regenerant for reaction, and oil gas is separated from the spent catalyst. The method tries to effectively inhibit the secondary reaction of the low-carbon olefin and improve the yield of the low-carbon olefin by separating the generated low-carbon olefin from the spent catalyst in time. However, it is difficult to satisfy the conversion rate of heavy oil and light hydrocarbon only by using a down-flow reactor and a riser reactor, and the maximization of the yield of low carbon olefin cannot be realized, and it can be seen from the examples of the patent that the ratio of the yield of low carbon olefin to the yield of dry gas is below 3, the raw material cannot be fully utilized, and the low-value product is high.

Chinese patent CN101210191A proposes a catalytic cracking process in which a downflow reactor and a riser reactor are connected in series. The preheated raw oil enters a descending reactor to contact with a high-temperature regenerated catalyst from a regenerator, is vaporized and is subjected to cracking reaction, oil gas discharged from an outlet of the descending reactor enters a riser reactor to continue reaction, another strand of regenerated catalyst is introduced from an inlet of the riser reactor, and the oil gas discharged from an outlet of the riser reactor and the catalyst enter a settling separator to be separated. According to different target products, different catalysts can be adopted in the riser reactor compared with the descending reactor, so that the gasoline yield can be improved, and the product quality can be improved. However, light hydrocarbons are not further converted, so the yield of light olefins is not very high.

Chinese patent CN102690682A proposes a catalytic cracking method for producing propylene, in which heavy raw material is contacted and reacted with a first catalyst using Y-type zeolite as active component in a first riser; and the light hydrocarbon and a second catalyst which takes shape-selective zeolite with the average pore diameter of less than 0.7nm as an active component are in contact reaction in the second riser reactor. Introducing the obtained oil gas into a fluidized bed reactor connected with the second reactor in series for reaction. The stripper of the catalytic cracking device is divided into two independent stripping zones by a partition plate, and the two stripping zones and the two risers form two independent reaction, stripping and regeneration routes respectively.

Disclosure of Invention

The invention aims to provide a process and a system for catalytic cracking by adopting double downers, which can improve the yield of low-carbon olefins and slow down the increase of the yield of dry gas.

In order to achieve the above object, the present invention provides a process for catalytic cracking using double downers, the process comprising:

a. feeding the heavy raw material into the upper part of a first descending tube reactor to contact with a first catalytic cracking catalyst from the top of the first descending tube reactor and carrying out a first catalytic cracking reaction from top to bottom to obtain a first product and a first semi-spent catalyst;

b. feeding the light raw material into the upper part of a second downer reactor to contact with a second catalytic cracking catalyst from the top of the second downer reactor and carrying out a second catalytic cracking reaction from top to bottom to obtain a second product and a second semi-spent catalyst;

c. and (c) feeding the first product and the first semi-finished catalyst obtained in the step (a) and the second product and the second semi-finished catalyst obtained in the step (b) into a fluidized bed reactor to contact with a third catalytic cracking catalyst and carry out a third catalytic cracking reaction to obtain a third product and a finished catalyst, and feeding the finished catalyst into a regenerator to regenerate to obtain a regenerated catalyst.

Optionally, the process further comprises step d:

and respectively feeding the regenerated catalyst in the regenerator as the first catalytic cracking catalyst, the second catalytic cracking catalyst and the third catalytic cracking catalyst into the top of the first downer reactor, the top of the second downer reactor and the fluidized bed reactor.

Optionally, in step d, based on the total weight of the regenerated catalyst leaving the regenerator in a unit time, 10 to 70 wt% of the regenerated catalyst is fed into the first downer reactor, 20 to 60 wt% of the regenerated catalyst is fed into the fluidized bed reactor, and 10 to 40 wt% of the regenerated catalyst is fed into the second downer reactor.

Optionally, the process further comprises: sending the third product into a product separation device for product separation to obtain dry gas, liquefied gas, gasoline, diesel oil and oil slurry;

and feeding the obtained gasoline and/or liquefied gas serving as the light raw material into the second downer reactor to perform the second catalytic cracking reaction.

Optionally, the process further comprises: and feeding the third product into a settling section at the upper part of the fluidized bed reactor for gas-solid separation, then feeding the third product out of the settling section, feeding the catalyst to be generated into a steam stripping section at the lower part of the fluidized bed reactor for steam stripping, and then feeding the catalyst into a regenerator.

Optionally, the conditions of the first catalytic cracking reaction include: the temperature is 510-690 ℃, the catalyst-oil ratio is 5-20, and the reaction time is 0.5-8 seconds;

the conditions of the second catalytic cracking reaction include: the temperature is 520 ℃ and 720 ℃, the catalyst-oil ratio is 8-26, and the reaction time is 1-10 seconds;

the conditions of the third catalytic cracking reaction include: the temperature is 480-650 ℃, and the weight hourly space velocity is 1-35 h^-1The reaction pressure is 0.15-0.35 MPa.

Optionally, the regenerated catalyst comprises a zeolite, an inorganic oxide, and optionally a clay; based on the weight of the regenerated catalyst, the content of the zeolite is 1-50 wt%, the content of the inorganic oxide is 5-99 wt%, and the content of the clay is 0-70 wt%;

the zeolite comprises a type-selective zeolite and a Y-type zeolite with the average pore diameter of less than 0.7 nanometer; the zeolite with the average pore diameter smaller than 0.7 nanometer is 25-90 wt% and the Y-type zeolite is 10-75 wt% based on the total weight of the zeolite, the zeolite with the average pore diameter smaller than 0.7 nanometer is at least one selected from ZSM series zeolite, ZRP zeolite, ferrierite, chabazite, dachiardite, erionite, A zeolite, column zeolite and turbid zeolite, and the Y-type zeolite is at least one selected from rare earth Y-type zeolite, rare earth hydrogen Y-type zeolite, ultrastable Y-type zeolite and rare earth ultrastable Y-type zeolite.

Optionally, the heavy feedstock is selected fromAt least one of vacuum wax oil, normal pressure wax oil, coking wax oil, deasphalted oil, furfural refined raffinate oil, coal liquefied oil, oil sand oil, shale oil, Fischer-Tropsch synthetic oil and animal and vegetable oil; the light raw material is gasoline and/or C rich in olefin₄A hydrocarbon.

Optionally, in the light raw material, C₄The weight ratio of the hydrocarbon to the gasoline rich in olefin is (0-2): 1, the weight ratio of the gasoline rich in olefins introduced into the second downer reactor to the heavy feedstock introduced into the first downer reactor is (0.05-0.30): 1.

the invention also provides a system for catalytic cracking by adopting double downer pipes, which comprises a first downer reactor, a fluidized bed reactor, a regenerator and a second downer reactor;

the first downer reactor is provided with a catalyst inlet positioned at the top, a heavy raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the second downer reactor is provided with a catalyst inlet positioned at the top, a light raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the fluidized bed reactor is provided with a catalyst inlet, a material inlet, a catalyst outlet and a product outlet, and the regenerator is provided with a catalyst inlet and a catalyst outlet;

the material outlet of the first downer reactor is communicated with the material inlet of the fluidized bed reactor, the material outlet of the second downer reactor is communicated with the material inlet of the fluidized bed reactor, the catalyst inlet of the regenerator is communicated with the catalyst outlet of the fluidized bed reactor, and the catalyst outlet of the regenerator is communicated with the catalyst inlet of the fluidized bed reactor, the catalyst inlet of the first downer reactor and the catalyst inlet of the second downer reactor.

Optionally, the system further comprises a product separation device, an inlet of the product separation device is communicated with a product outlet of the fluidized bed reactor, the product separation device is provided with a dry gas outlet, a liquefied gas outlet, a gasoline outlet, a diesel oil outlet and an oil slurry outlet, and a liquefied gas outlet and/or a gasoline outlet of the product separation device is communicated with a light raw material inlet of the second downer reactor.

The invention is based on the combined reactor formed by the first downer reactor, the fluidized bed reactor and the second downer reactor, realizes the catalytic cracking of different feeds in the proper reactor by optimizing the process scheme and preparing the proper catalyst, effectively improves the conversion rate of heavy oil, promotes the cracking of light raw materials again, obviously increases the yield of low-carbon olefin, and simultaneously slows down the increase of the yield of dry gas.

The invention arranges a first downer reactor and a fluidized bed reactor along the flowing direction of reaction materials. By utilizing the first downer reactor, the catalyst back-mixing phenomenon in the traditional riser reactor can be avoided to the maximum extent, and the catalyst activity is improved. The high-temperature regenerated catalyst from the regenerator is supplemented to the inlet of the fluidized bed reactor to regulate and control the severity (including reaction temperature and catalyst-to-oil ratio) of the fluidized bed reactor, the capability of effectively cracking heavy raw materials into low-carbon olefin and gasoline olefin in the fluidized bed reactor is enhanced, and a reaction product is separated from the carbon-deposited spent catalyst through a high-efficiency gas-solid separation device in a settling section, so that the heavy raw materials can be effectively cracked into propylene and gasoline, and meanwhile, the re-cracking reaction of the low-carbon olefin, particularly the propylene after generation is inhibited.

The invention relates to gasoline and/or C rich in olefin₄Hydrocarbons are introduced into the second descending tube reactor, and the second descending tube can also avoid the catalyst back-mixing phenomenon in the traditional riser reactor to the maximum extent, improve the activity of the catalyst, promote the catalytic cracking of light gasoline, improve the yield of low-carbon olefins and simultaneously slow down the improvement of the yield of dry gas. The carbon deposit amount of the catalyst is less in the reaction process of the light raw material, and the spent catalyst still has higher activity and can be introduced into the fluidized bed reactor to contact with the heavy raw material and promote the reaction of the heavy raw material.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 includes a schematic flow diagram of one embodiment of the process of the present invention and also includes a schematic structural diagram of one embodiment of the system of the present invention.

Description of the reference numerals

1 catalyst tank 2 first downer reactor 3 fluidized bed reactor

4 settling section, 5 stripping section and 6 to-be-grown inclined pipes

7 regenerator 8 regeneration inclined tube 9 second downer reactor

10 catalyst jar 11 regeneration pipe chute 12 result separator

13 regeneration inclined pipe 14 pipeline 15 pipeline

16 line 17 line 18 line

19 line 20 line 21 line

22 line 23 line 24 line

25 line 26 line 27 line

28 pipeline

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

As shown in fig. 1, the present invention provides a catalytic cracking process using double downers, comprising: a. feeding the heavy raw material into the upper part of a first descending tube reactor 2 to contact with a first catalytic cracking catalyst from the top of the first descending tube reactor 2 and carrying out a first catalytic cracking reaction from top to bottom to obtain a first product and a first semi-spent catalyst; b. feeding the light raw material into the upper part of a second downgoing tube reactor 9 to contact with a second catalytic cracking catalyst from the top of the second downgoing tube reactor 9 and carrying out a second catalytic cracking reaction from top to bottom to obtain a second product and a second semi-spent catalyst; c. and (3) feeding the first product and the first semi-finished catalyst obtained in the step (a) and the second product and the second semi-finished catalyst obtained in the step (b) into the fluidized bed reactor 3 to contact with a third catalytic cracking catalyst and carry out a third catalytic cracking reaction to obtain a third product and a to-be-regenerated catalyst, and feeding the to-be-regenerated catalyst into a regenerator 7 to be regenerated to obtain a regenerated catalyst. The process can improve the yield of the low-carbon olefin and simultaneously slow down the increase of the yield of the dry gas.

According to the invention, the spent catalyst needs to be regenerated, as is well known to the person skilled in the art, and therefore the process may also comprise: and (3) feeding the third product into a settling section 4 at the upper part of the fluidized bed reactor 3 for gas-solid separation, then feeding the third product out of the settling section 4, feeding the catalyst to be generated into a steam stripping section 5 at the lower part of the fluidized bed reactor 3 for steam stripping, and then feeding the catalyst to be generated into a regenerator 7, wherein the process further comprises the following steps: and feeding the regenerated catalyst in the regenerator 7 as the first catalytic cracking catalyst, the second catalytic cracking catalyst and the third catalytic cracking catalyst into the top of the first downer reactor 2, the top of the second downer reactor 9 and the fluidized bed reactor 3 respectively. It should be noted that, in order to promote the catalytic cracking reaction, the regenerated catalysts for the first catalytic cracking catalyst, the second catalytic cracking reaction and the third catalytic cracking reaction, which are all uncooled catalysts, are sent into each reactor to produce a large amount of light olefins, i.e., the temperature is between 500 ℃ and 900 ℃, preferably between 600 ℃ and 800 ℃.

According to the raw materials, regenerated catalyst with different weights can be selectively fed into the fluidized bed reactor 3, the first downer reactor 2 and the second downer reactor 9 from the regenerator 7, and the reaction conditions can be optimized, in the step d, more than 0 to less than 100 wt%, preferably 10 to 70 wt% of the regenerated catalyst can be fed into the first downer reactor 2, more than 0 to less than 100 wt%, preferably 20 to 60 wt% of the regenerated catalyst can be fed into the fluidized bed reactor 3, and more than 0 to less than 100 wt%, preferably 10 to 40 wt% of the regenerated catalyst can be fed into the second downer reactor 9, based on the total weight of the regenerated catalyst leaving the regenerator per unit time.

The invention carries out catalytic cracking on light raw materials in the second downer reactor 9 and the fluidized bed reactor 3, and carries out catalytic cracking on heavy raw materials in the first downer reactor 2 and the fluidized bed reactor 3 in sequence, thereby not only respectively carrying out catalytic cracking on different raw materials and improving the selectivity of a target product, but also sending the second semi-spent catalyst with lower carbon content obtained by the cracking reaction of the light raw materials into the fluidized bed reactor 3 again for cracking, and sending the regenerated catalyst into the fluidized bed reactor to improve the average activity of the catalyst and increase the conversion rate of the catalytic cracking of the first downer reactor 2 and the fluidized bed reactor 3.

According to the present invention, in order to separate the third product, the process may further include: and sending the third product to a product separation device 12 for product separation to obtain dry gas, liquefied gas, gasoline, diesel oil and oil slurry. The product separation unit 12 is well known to those skilled in the art and may be a fractionation column or the like.

According to the present invention, the process may further comprise, in order to convert light hydrocarbons in the catalytic cracking product: and feeding the obtained gasoline and/or liquefied gas as the light raw material into the second downer reactor 9 to perform the second catalytic cracking reaction.

According to the present invention, catalytic cracking is a well-known process to those skilled in the art, and the description of the invention is omitted, and the conditions of the first catalytic cracking reaction may include: the temperature (outlet at the bottom of the first downer reactor) is 510-690 ℃, preferably 520-650 ℃, the catalyst-oil ratio is 5-20, preferably 7-18, the weight of the atomized water vapor of the heavy raw material feeding accounts for 2-50 wt%, preferably 5-15 wt%, the reaction time is 0.5-8 seconds, preferably 1.5-4 seconds, the ratio of the catalyst introduced into the first downer reactor and the fluidized bed reactor is 1: (1-3); the conditions of the second catalytic cracking reaction may include: the temperature (outlet at the bottom of the second downer reactor) is 520-720 ℃, preferably 530-700 ℃, the catalyst-oil ratio is 8-26, preferably 10-24, and the weight is lightThe atomized water vapor in the raw material feeding accounts for 2-50 wt%, preferably 5-15 wt% of the total weight of the light raw material and the atomized water vapor, and the reaction time is 1-10 seconds, preferably 2-7 seconds; the conditions of the third catalytic cracking reaction may include: the temperature is 480-650 ℃, preferably 500-640 ℃, and the weight hourly space velocity is 1-35 hours^-1Preferably 2 to 33 hours^-1The ratio of the catalyst to the oil is 6-20, preferably 7-18, and the reaction pressure (absolute pressure, outlet pressure) is 0.15-0.35 MPa, preferably 0.2-0.35 MPa.

The catalysts used for catalytic cracking according to the present invention are well known to those skilled in the art, and in the case of regenerated catalysts, the catalyst in said regenerated catalysts may be one or a combination of several of the catalysts provided by the prior art, and may be commercially available or prepared according to known methods. In one embodiment, the regenerated catalyst may include a zeolite, an inorganic oxide, and optionally a clay; the zeolite may be present in an amount of 1 to 50 wt%, the inorganic oxide may be present in an amount of 5 to 99 wt%, and the clay may be present in an amount of 0 to 70 wt%, based on the weight of the regenerated catalyst. In addition, in order to increase the propylene yield and increase the conversion, the zeolite may include a type-selective zeolite and a type-Y zeolite having an average pore diameter of less than 0.7 nm; the zeolite type having an average pore size of less than 0.7nm may be present in an amount of from 25 to 90 wt%, preferably from 40 to 60 wt%, and the zeolite type Y may be present in an amount of from 10 to 75 wt%, preferably from 30 to 60 wt%, on a dry basis and based on the total weight of the zeolite. The zeolite with average pore diameter less than 0.7nm may be at least one selected from ZSM series zeolite, ZRP zeolite, ferrierite, chabazite, dachiardite, erionite, A zeolite, epistilbite and turbid zeolite, and one or more physically and/or chemically treated zeolite. The ZSM-series zeolite may be one or a mixture of two or more selected from ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other zeolites of similar structure. For more details on ZSM-5 see USP3702886 and for more details on ZRP see USP5232675, CN1211470A, CN 1611299A. The Y-type zeolite can be selected from rare earth Y-type zeolite (REY), rare earth hydrogen Y-type zeolite (REHY), and ultrastable Y-type zeoliteAt least one of zeolite (USY) and rare earth ultrastable Y-type zeolite (REUSY). The inorganic oxide may be silicon dioxide (SiO) as a binder₂) And/or aluminum oxide (Al)₂O₃). The clay selected as a matrix, i.e., carrier, may be kaolin and/or halloysite.

Heavy feedstocks, which are well known to those skilled in the art according to the present invention, are, for example, heavy hydrocarbons, which may be one or a mixture of more than one selected from petroleum hydrocarbons, mineral oils and synthetic oils, and/or various animal and vegetable oil-based feedstocks rich in hydrocarbons. The petroleum hydrocarbon can be vacuum wax oil, atmospheric residue, vacuum wax oil blended part vacuum residue or other hydrocarbon oil obtained by secondary processing, such as one or more of coker wax oil, deasphalted oil and furfural refined raffinate oil. The mineral oil can be one or more selected from coal liquefied oil, oil sand oil and shale oil. The synthetic oil can be distillate oil obtained by F-T synthesis of coal, natural gas or asphalt. The various animal and vegetable oils rich in hydrocarbon can be various animal and vegetable oils. The heavy raw material is preferably at least one of vacuum wax oil, normal pressure wax oil, coking wax oil, deasphalted oil, furfural refined raffinate oil, coal liquefied oil, oil sand oil, shale oil, Fischer-Tropsch synthetic oil and animal and vegetable oil.

According to the invention, the light feedstock introduced into the second downer reactor is preferably an olefin-rich gasoline and/or C₄Hydrocarbons, which may be selected from gasoline fractions produced by the process and/or gasoline fractions produced by other units. The gasoline fraction produced by other equipment can be one or more than one of catalytic cracking crude gasoline, catalytic cracking stable gasoline, coker gasoline, visbreaker gasoline and other gasoline fractions produced by oil refining or chemical process, preferably gasoline fraction produced by said process. The olefin content of the olefin-rich gasoline may be 25 to 95% by weight, preferably 35 to 90% by weight, and most preferably 50% by weight or more. The end point of the olefin-rich gasoline is not more than 204 ℃, and can be, for example, a distillation range of 35-The full boiling range gasoline fraction of 204 deg.C may be narrow fraction thereof, such as gasoline fraction with final boiling point not higher than 85 deg.C, preferably gasoline fraction with boiling range of 40-85 deg.C. Said C is₄By hydrocarbon is meant₄The low molecular hydrocarbon containing C4 alkane, olefin and alkyne existing in gas form at normal temperature and normal pressure with fraction as main component may be C-rich hydrocarbon produced by the present process₄The gaseous hydrocarbon products of the fraction can also be C-rich products produced by other plant processes₄Gaseous hydrocarbons of the fraction, of which C self-produced by the process is preferred₄And (6) cutting. Said C is₄The olefin content of the hydrocarbon is more than 50% by weight, preferably more than 60% by weight, and most preferably 70% by weight or more. In the light raw material, C₄The weight ratio of hydrocarbons to olefin-rich gasoline may be (0-2): 1, preferably (0-1.2): 1, more preferably (0-0.8): 1; the weight ratio of the olefin-rich gasoline introduced into the second downer reactor to the heavy feedstock introduced into the first downer reactor may be (0.05-0.30): 1, preferably (0.10-0.20): 1.

according to the invention, the outlet of the downer reactor is preferably a low pressure outlet distributor, which may have a pressure drop of less than 10KPa, and which may be an existing distributor, such as an arch distributor or the like.

According to the invention, steam and oil gas obtained by reaction are introduced into the bottom of the fluidized bed reactor in the steam stripping section and discharged out of the reactor after passing through the fluidized bed reactor, so that the partial pressure of the oil gas can be reduced, the retention time of the oil gas in the settling section is shortened, and the yield of propylene is increased.

As shown in fig. 1, the present invention also provides a system for catalytic cracking using dual downers, comprising a first downer reactor 2, a fluidized bed reactor 3, a regenerator 7, and a second downer reactor 9; the first downer reactor 2 is provided with a catalyst inlet positioned at the top, a heavy raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the second downer reactor 9 is provided with a catalyst inlet positioned at the top, a light raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the fluidized bed reactor 3 is provided with a catalyst inlet, a material inlet, a catalyst outlet and a product outlet, and the regenerator 7 is provided with a catalyst inlet and a catalyst outlet; the material outlet of the first downer reactor 2 is communicated with the material inlet of the fluidized bed reactor 3, the material outlet of the second downer reactor 9 is communicated with the material inlet of the fluidized bed reactor 3, the catalyst inlet of the regenerator 7 is communicated with the catalyst outlet of the fluidized bed reactor 3, and the catalyst outlet of the regenerator 7 is communicated with the catalyst inlet of the fluidized bed reactor 3, the catalyst inlet of the first downer reactor 2 and the catalyst inlet of the second downer reactor 9.

According to the invention, the downer reactor can be one or the combination of two of a constant diameter downer, a constant linear speed downer and a variable diameter downer. The fluidized bed reactor may be one selected from a fixed fluidized bed, a bulk fluidized bed, a bubbling bed, a turbulent bed, a fast bed, a transport bed, and a dense bed reactor.

According to the present invention, as shown in fig. 1, the system may further include a product separation device 12, an inlet of the product separation device 12 is communicated with a product outlet of the fluidized bed reactor 3, and the product separation device 12 is provided with a dry gas outlet, a liquefied gas outlet, a gasoline outlet, a diesel oil outlet, and an oil slurry outlet. The product separation device can be the prior art, and the invention has no special requirement. And the third product and the spent catalyst which leave the fluidized bed reactor enter a settling section, and after the spent catalyst carried in the settling section is settled and separated, the third product is introduced into a subsequent product separation device. In the product separation device, the third product is separated to obtain dry gas, liquefied gas, gasoline, diesel oil and oil slurry.

According to the present invention, in order to increase the propylene yield, the liquefied gas outlet and/or the gasoline outlet of the product separation unit 12 may be in communication with the light feedstock inlet of the second downer reactor 9.

In order to facilitate the separation of the product and the regeneration of the catalyst to be regenerated, the fluidized bed reactor 3 may include a bed reaction section, a stripping section 5 disposed below the bed reaction section, and a settling section 4 disposed above the bed reaction section, the stripping section 5, and the settling section 4 may be coaxially disposed and fluidly connected, the bed reaction section may be provided with a catalyst inlet and a material inlet of the fluidized bed reactor 3, the top of the settling section 4 may be provided with a product outlet of the fluidized bed reactor 3, and the lower portion of the stripping section 5 may be provided with a catalyst outlet of the fluidized bed reactor 3.

The process provided by the present invention is further described below with reference to the accompanying drawings.

As shown in fig. 1, the high-temperature regenerated catalyst is introduced into the catalyst tank 10 of the second downer reactor 9, the catalyst tank 1 of the first downer reactor 2, and the fluidized-bed reactor 3 through the regeneration inclined tube 8, the regeneration inclined tube 11, and the regeneration inclined tube 13, respectively. The preheated heavy raw material is mixed with atomized steam from a pipeline 15 according to a certain proportion through a pipeline 14, then the mixture is injected into the first downer reactor 2 to be contacted with a high-temperature regenerant which passes through the regeneration inclined pipe 13 and is lifted by lifting gas from a pipeline 27, the first catalytic cracking reaction is carried out, and the mixture of the first product and the first spent catalyst passes through an outlet distributor (not marked in the figure) of the first downer reactor 2 and the fluidized bed reactor 3. Preheated or not preheated gasoline fraction rich in olefin and/or C4 hydrocarbon is mixed with atomized steam from a pipeline 19 according to a certain proportion through a pipeline 18, injected into a second downer reactor 9, mixed with a high-temperature regenerated catalyst lifted by lift gas from a pipeline 28 through a regeneration inclined tube 8 and subjected to a second catalytic cracking reaction, a second product and a second semi-spent catalyst mixture are introduced into a fluidized bed reactor 3 through an outlet distributor (not marked in the figure) of the second downer reactor 9, mixed with the high-temperature regenerated catalyst flowing in through the regeneration inclined tube 11 and subjected to a third catalytic cracking reaction, and finally enters a settling section 4 to separate the third product from the spent catalyst; the third product obtained by separation enters the subsequent product separation unit 12 through a line 20. The reaction products are separated in product separation unit 12 into gaseous hydrocarbons (withdrawn via line 22), gasoline (withdrawn via line 23), diesel (withdrawn via line 24), light cycle oil (withdrawn via line 25) and slurry oil (withdrawn via line 26). The gaseous hydrocarbons exiting line 22 may be separated and refined to produce polymer grade propylene product and an olefin rich C4 fraction, wherein the olefin rich C4 fraction may be returned to the reactor for conversion to ethylene and propylene. The gasoline led out from the pipeline 23 can be partially or completely returned to the reaction system for conversion, or the gasoline can be cut into light gasoline and heavy gasoline distillation sections, the light gasoline is partially or completely returned to the reaction system for conversion, and the light gasoline is preferably returned to the second descending tube reactor for conversion; the catalyst obtained by separation in the settling section enters a bed layer reaction zone and then enters a stripping section 5, stripping steam is injected through a pipeline 16 and is in countercurrent contact with the carbon-deposited spent catalyst, reaction oil gas carried by the spent catalyst is stripped as much as possible, and then the reaction oil gas is introduced into a settler through the bed layer reaction zone and is led out of the reactor together with other oil gas through a pipeline 20. The stripped catalyst is sent to a regenerator 7 through a to-be-regenerated inclined pipe 6 for coke burning regeneration. Oxygen-containing gas is injected into the regenerator 7 via line 17 and regeneration flue gas is withdrawn via line 21. The regenerated catalyst enters different reactors for recycling through a regeneration inclined tube 8, a regeneration inclined tube 11 and a regeneration inclined tube 13. In the above embodiment process, the pre-lift media introduced into line 28 and line 27 may be selected from steam, C1-C4 hydrocarbons or conventional catalytic cracking dry gas, steam being preferred in the present invention.

The following examples further illustrate the invention but are not intended to limit the invention thereto.

The raw oil and the catalyst used in the examples and comparative examples were the same. The feedstock A used was a cracking feedstock, the specific properties of which are shown in Table 1. The adopted catalyst is MMC-2 produced by China petrochemical Qilu catalyst factory, contains selective zeolite with the average pore diameter of less than 0.7 nanometer and Y-type molecular sieve, and the specific properties are shown in Table 2.

Comparative example 1

The tests were carried out in a medium-sized catalytic cracking unit. The device comprises a set of independent reaction regeneration system: the reactor is a first downer reactor and a fluidized bed combined reactor, the inner diameter of the first downer is 16 mm, the length of the first downer reactor is 3200 mm, the fluidized bed reactor is connected in series at the outlet of the bottom of the first downer reactor, the diameter (inner diameter) of the fluidized bed reactor is 64 mm, and the height of the fluidized bed reactor is 600 mm. The catalyst used is MMC-2 catalyst, and the raw materials shown in Table 1 are cracked; the reacted oil gas is separated from the catalyst, the catalyst enters a stripper for steam stripping and then enters a regenerator for regeneration, the regenerated catalyst leaves the regenerator in two paths, and one path enters the fluidized bed reactor, so that the reaction temperature and the catalyst-to-oil ratio in the fluidized bed reactor are improved. The other path enters a catalyst tank at the top of the first downer reactor; oil gas enters a product separation device. The reaction conditions and the reaction results are shown in tables 3 and 4.

Comparative example 2

The tests were carried out in a medium-sized catalytic cracking unit. The device comprises a set of independent reaction regeneration system: the reactor is a riser reactor and a fluidized bed combined reactor, the inner diameter of the riser is 16 mm, the length of the riser is 3200 mm, the outlet at the top of the riser reactor is connected with the fluidized bed reactor in series, the diameter (inner diameter) of the fluidized bed reactor is 64 mm, and the height of the fluidized bed reactor is 600 mm. The catalyst used is MMC-2 catalyst, and the raw materials shown in Table 1 are cracked; separating oil gas from catalyst after reaction, feeding the catalyst into a stripper for steam stripping, then feeding the catalyst into a regenerator for regeneration, and then feeding the catalyst into the riser reactor again for reaction; the reaction product from the fluidized bed reactor is fed to a product separation unit. The reaction conditions and the reaction results are shown in tables 3 and 4.

Example 1

Referring to comparative example 1, as shown in fig. 1, except that the regenerated catalyst leaves the regenerator in three paths, one path entering the fluidized bed reactor, the other path entering the catalyst tank at the top of the first downer reactor, and the third path entering the second downer reactor. The inner diameter of the second downer reactor is 12 mm, the length of the second downer reactor is 2200 mm, the adopted catalyst is MMC-2 catalyst, light gasoline (the distillation range is 30-85 ℃, the olefin content is 52 wt%, and the weight accounts for 15 wt% of the heavy raw material) which is rich in olefin and comes from a product separation device is used as the light raw material to be cracked, and the obtained oil-gas and catalyst mixture enters the fluidized bed reactor to be cracked again. The catalyst obtained by separation is sent to a regenerator for coke burning regeneration, and the oil gas product obtained by separation and the oil gas product from a settler are mixed and enter a product separation device. The reaction conditions and the reaction results are shown in tables 3 and 4.

As can be seen from tables 3 and 4, compared with the riser reactor and the fluidized bed reactor of comparative example 2, the first downer reactor and the fluidized bed reactor of comparative example 1 and example 1 can alleviate adverse effects such as catalyst backmixing in the riser reactor, improve the yield of the low carbon olefins, and alleviate the increase of the dry gas yield. The introduction of the regenerant into the fluidized bed reactor connected in series with the first downer reactor can improve the average activity and reaction temperature of the catalyst in the fluidized bed reactor, and improve the heavy oil conversion rate and the low carbon olefin yield. The light raw material in the second downer reactor of example 1 contacts with the high-temperature catalyst, so that the conversion rate of the light raw material is ensured, the yield of the low-carbon olefin is improved, the increase of the yield of the dry gas can be slowed down, and the ratio of the low-carbon olefin to the yield of the dry gas is increased.

The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the content of the present invention as long as it does not depart from the gist of the present invention.

TABLE 1

Item	Starting materials A
		Density (C)20 ℃ C, g.cm^-3	0.91
Freezing point, deg.C	34
		Four components, by weight%
Saturation fraction	72.6
		Aromatic component	20.9
Glue	6.3
		Asphaltenes	0.2
The element composition by weight percent
		Carbon (C)	86.86
Hydrogen	12.62
		Sulfur	0.46
Nitrogen is present in	0.15
		Distilling range-℃
Initial boiling point	271
		10% by weight	362
30% by weight	406
		50% by weight	437
70% by weight	466
		90% by weight	/

TABLE 2

Name of catalyst	MMC-2
		The main active component	USY+ZRP
Chemical property, weight%
		Al₂O₃	52.3
Na₂O	0.072
		RE₂O₃	0.82
Physical Properties
		Total pore volume, ml/g	0.183
Micropore volume, ml/g	0.024
		Specific surface area, rice²Per gram	143
Specific surface area of zeolite, rice²Per gram	50
		Specific surface area of substrate, rice²Per gram	105
Bulk density, g/ml	0.83
		Micro-inverse activity, weight%	67

Table 3 shows the reaction conditions of example 1 and comparative examples 1 to 2

Case numbering	Example 1	Comparative example 1	Example 2
				First down-flow tube (riser) reactor	Down pipe	Lifting pipe	Down pipe
Heavy feedstock	Starting materials A	Starting materials A	Starting materials A
				Catalyst and process for preparing same	MMC-1	MMC-1	MMC-1
Reactor outlet temperature,. deg.C	570	570	570
				Reaction time in seconds	1.5	1.5	1.5
Weight ratio of solvent to oil	12.5	12.5	12.5
				Fluidized bed reactor
Weight hourly space velocity, hours^-1	3	3	3
				Reaction temperature of	580	550	580
Settler pressure, megapascals (absolute pressure)	0.21	0.21	0.21
				Second downer reactor
Light raw material	/	/	Light gasoline
				Catalyst and process for preparing same	/	/	MMC-1
Riser outlet temperature,. deg.C	/	/	650
				Weight ratio of solvent to oil			22
Reaction time in seconds	/	/	2.1
				Mass ratio of light gasoline to heavy raw material	/	/	0.15:1

Table 4 shows the results of the reactions of example 1 and comparative examples 1 to 2

Claims

1. A process for catalytic cracking using dual downcomer, the process comprising:

a. feeding the heavy raw material into the upper part of a first descending tube reactor (2) to contact with a first catalytic cracking catalyst from the top of the first descending tube reactor (2) and carrying out a first catalytic cracking reaction from top to bottom to obtain a first product and a first semi-spent catalyst;

b. feeding the light raw material into the upper part of a second downer reactor (9) to contact with a second catalytic cracking catalyst from the top of the second downer reactor (9) and carrying out a second catalytic cracking reaction from top to bottom to obtain a second product and a second semi-spent catalyst;

c. and (3) feeding the first product and the first semi-spent catalyst obtained in the step (a) and the second product and the second semi-spent catalyst obtained in the step (b) into a fluidized bed reactor (3) to contact with a third catalytic cracking catalyst for a third catalytic cracking reaction to obtain a third product and a spent catalyst, and feeding the spent catalyst into a regenerator (7) for regeneration to obtain a regenerated catalyst, wherein the third catalytic cracking catalyst is a regenerated catalyst which is from the regenerator (7) and is not cooled, and the temperature is 500-900 ℃.

2. The process of claim 1, further comprising step d:

and (3) taking the regenerated catalyst in the regenerator (7) as the first catalytic cracking catalyst, the second catalytic cracking catalyst and the third catalytic cracking catalyst, and respectively feeding the regenerated catalyst into the top of the first downer reactor (2), the top of the second downer reactor (9) and the fluidized bed reactor (3).

3. The process according to claim 2, step d, wherein from 10 to 70% by weight of the regenerated catalyst is fed to the first downer reactor (2), from 20 to 60% by weight of the regenerated catalyst is fed to the fluidized bed reactor (3), and from 10 to 40% by weight of the regenerated catalyst is fed to the second downer reactor (9), based on the total weight of the regenerated catalyst leaving the regenerator per unit time.

4. The process of claim 1, further comprising: sending the third product into a product separation device (12) for product separation to obtain dry gas, liquefied gas, gasoline, diesel oil and oil slurry;

and feeding the obtained gasoline and/or liquefied gas as the light raw material into the second downer reactor (9) for the second catalytic cracking reaction.

5. The process of claim 1, further comprising: and feeding the third product into a settling section (4) at the upper part of the fluidized bed reactor (3) for gas-solid separation, then feeding the third product out of the settling section (4), feeding the catalyst to be generated into a steam stripping section (5) at the lower part of the fluidized bed reactor (3), steam stripping, and then feeding the third product into a regenerator (7).

6. The process of claim 1, wherein the conditions of the first catalytic cracking reaction include: the temperature is 510-690 ℃, the catalyst-oil ratio is 5-20, and the reaction time is 0.5-8 seconds;

7. The process of claim 1, wherein the regenerated catalyst comprises a zeolite, an inorganic oxide, and optionally a clay; based on the weight of the regenerated catalyst, the content of the zeolite is 1-50 wt%, the content of the inorganic oxide is 5-99 wt%, and the content of the clay is 0-70 wt%;

8. The process of claim 1, wherein the heavy feedstock is at least one selected from the group consisting of vacuum wax oil, atmospheric wax oil, coker wax oil, deasphalted oil, furfural refined raffinate oil, coal liquefaction oil, oil sand oil, shale oil, fischer-tropsch synthesis oil, and animal and vegetable fats; the light raw material is gasoline and/or C rich in olefin₄A hydrocarbon.

9. The process of claim 8, wherein in the light feedstock, C₄The weight ratio of the hydrocarbon to the gasoline rich in olefin is (0-2): 1, the weight ratio of the gasoline rich in olefins introduced into the second downer reactor to the heavy feedstock introduced into the first downer reactor is (0.05-0.30): 1.

10. a system for catalytic cracking by using double downer pipes comprises a first downer reactor (2), a fluidized bed reactor (3), a regenerator (7) and a second downer reactor (9);

the first downer reactor (2) is provided with a catalyst inlet positioned at the top, a heavy raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the second downer reactor (9) is provided with a catalyst inlet positioned at the top, a light raw material inlet positioned at the upper part and a material outlet positioned at the bottom, the fluidized bed reactor (3) is provided with a catalyst inlet, a material inlet, a catalyst outlet and a product outlet, and the regenerator (7) is provided with a catalyst inlet and a catalyst outlet;

the material outlet of the first downer reactor (2) is communicated with the material inlet of the fluidized bed reactor (3), the material outlet of the second downer reactor (9) is communicated with the material inlet of the fluidized bed reactor (3), the catalyst inlet of the regenerator (7) is communicated with the catalyst outlet of the fluidized bed reactor (3), and the catalyst outlet of the regenerator (7) is communicated with the catalyst inlet of the fluidized bed reactor (3), the catalyst inlet of the first downer reactor (2) and the catalyst inlet of the second downer reactor (9).

11. The system according to claim 10, wherein the system further comprises a product separation device (12), an inlet of the product separation device (12) being in communication with a product outlet of the fluidized bed reactor (3), the product separation device (12) being provided with a dry gas outlet, a liquefied gas outlet, a gasoline outlet, a diesel outlet and a slurry oil outlet, the liquefied gas outlet and/or the gasoline outlet of the product separation device (12) being in communication with the light feedstock inlet of the second downer reactor (9).