CN109694739B

CN109694739B - Method and device for preparing low-carbon olefin by cracking crude oil

Info

Publication number: CN109694739B
Application number: CN201711002031.0A
Authority: CN
Inventors: 石莹; 李蔚; 张兆斌; 周丛; 张利军; 杜志国; 王国清; 张永刚
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2017-10-24
Filing date: 2017-10-24
Publication date: 2021-05-11
Anticipated expiration: 2037-10-24
Also published as: CN109694739A

Abstract

The invention belongs to the field of low-carbon olefin preparation, and discloses a method and a device for preparing low-carbon olefin by cracking crude oil. The method comprises the following steps: 1) the crude oil is sent into a first pipe group of a convection section for preheating, and the preheated crude oil is subjected to gas-liquid separation through a first cyclone separator to form a first vapor phase and a first liquid phase; 2) hydroprocessing the first liquid phase, and mixing the hydroprocessed first liquid phase with liquid hydrocarbon to obtain a mixture; 3) the mixture is sent into a first tube group of a convection section of the cracking furnace for preheating, and the preheated mixture is subjected to gas-liquid separation through a second cyclone separator to form a second vapor phase and a second liquid phase; 4) the first vapor phase and the second vapor phase are sent to a second tube group of a convection section of the cracking furnace, heated to a cross temperature and then directly sent to a radiation section for cracking to generate cracking gas containing low-carbon olefin; 5) the second liquid phase is contacted with superheated steam from the convection section for stripping. The method of the invention can improve the cracking efficiency of crude oil and increase the yield of olefin products.

Description

Method and device for preparing low-carbon olefin by cracking crude oil

Technical Field

The invention relates to the field of preparation of low-carbon olefins, in particular to a method and a device for preparing low-carbon olefins by cracking crude oil.

Background

The low-carbon olefin is generally referred to as unsaturated hydrocarbon with four carbon atoms or less, mainly comprises organic chemical raw materials with high economic value, such as ethylene, propylene, isobutene, butadiene and the like, and with the development of economy in China, the demand of the organic chemical raw materials is increased year by year, and although the production scale of the low-carbon olefin is also increased year by year, the increased demand cannot be met. Therefore, the technology for effectively improving the yield of the low-carbon olefin has wide application prospect.

For a long time, China always prepares low-carbon olefin products from naphtha. However, in recent years, along with the mass exploitation of middle east oilfield associated gas and U.S. shale gas, these cheap oil and gas resources are used in large quantities as ethylene raw materials, which causes a sharp drop in the price of ethylene-related products. In order to cope with the impact of market competition, the raw material source of the ethylene cracking device is expanded, the raw material cost is reduced, and the method becomes an effective means for cost reduction and efficiency improvement of the traditional ethylene enterprises. Therefore, the special heavy hydrocarbon, especially unprocessed crude oil, is used as the raw material of the cracking furnace to produce the low-carbon olefin, which is beneficial to reducing the raw material cost and energy consumption of an olefin production device and is quickly adapted to the supply and demand change of the cracking raw material in the market.

Crude oil is generally divided into four components, a saturates, an aromatics, a gums and asphaltenes, wherein saturates and asphaltenes represent the most stable and the least stable components of the crude oil, respectively. The crude oil contains high molecular weight nonvolatile components with the boiling point of more than 590 ℃, and when the convection section of a conventional ethylene cracking furnace is preheated, a small part of the nonvolatile components are not gasified, and the unvaporized nonvolatile components are carried to the radiation section along with the mixed gas flow, so that coking deposition of the radiation section is easily caused, even the radiation section is blocked, and the yield of cracked products is influenced.

In order to improve the yield of low-carbon olefin and utilize crude oil resources to the maximum extent, US3617493 and CN1957068A disclose methods for treating crude oil by using a steam cracking device, wherein an external flash tank is used for treating crude oil preheated in a convection section of a cracking furnace, after gas-liquid separation is realized, a gas phase enters a radiation section for cracking, and a liquid phase can be used as bunker fuel oil. Wherein, after flash evaporation, 5 percent of hydrocarbon raw materials are remained in liquid, the flash evaporation separation efficiency is lower, and the flash evaporator device occupies larger space and has low space utilization rate.

CN1018552B and US5580443 disclose a process for treating a low grade feedstock containing a large amount of heavy fractions with a cracking furnace. The raw material is pumped out in the middle of the convection section, then mixed with a certain amount of superheated dilution steam, separated from heavy fraction by gas-liquid separation, returned to the convection section, and sent to the radiation section for decomposition. Wherein, the low-grade raw materials are mixed with steam and then are subjected to flash separation, only 5 to 20 percent of liquid can be separated, and the separation efficiency is lower.

In the above patent documents, the vapor-liquid separation is carried out by using a flash vessel as a method for treating the effluent in the convection section, but the separation efficiency in the flash vessel is low for the vapor-liquid separation of the heavy raw material, and the vessel type separation equipment such as the flash vessel is large in volume, heavy in weight, and wide in floor space, and is not suitable for the case of small space.

Therefore, it is highly desirable to provide a crude oil cracking method which can effectively improve the crude oil cracking efficiency, increase the yield of low carbon olefin products, and reduce the coking and blockage of the cracking device in the radiant section and the quenching section, thereby reducing the operation cost.

Disclosure of Invention

In view of the above problems in the prior art, the present invention is to provide a method for preparing low carbon olefins by cracking crude oil, and an apparatus for preparing low carbon olefins by cracking crude oil. The method overcomes the defects that the crude oil is easy to coke and even block at the radiation degree and quenching part of a cracking furnace when the crude oil is directly subjected to steam cracking by combining the processes of hydroprocessing, mixing with light raw materials, gas-liquid separation by adopting a cyclone separator and the like, and can effectively improve the cracking efficiency of the crude oil and increase the yield of olefin products.

The first aspect of the invention provides a method for preparing low-carbon olefins by cracking crude oil, which comprises the following steps:

1) sending crude oil into a first tube group of a convection section of a cracking furnace for preheating, and performing gas-liquid separation on the preheated crude oil through a first cyclone separator to form a first vapor phase and a first liquid phase;

2) hydroprocessing the first liquid phase, and then mixing with liquid hydrocarbons to obtain a mixture;

3) sending the mixture into a first tube group of a convection section of a cracking furnace for preheating, and performing gas-liquid separation on the preheated mixture through a second cyclone separator to form a second vapor phase and a second liquid phase;

4) sending the first vapor phase and the second vapor phase into a second tube group of a convection section of the cracking furnace, heating to a cross temperature, and directly sending into a radiation section for cracking to generate cracking gas containing low-carbon olefin;

5) the second liquid phase is contacted with superheated steam from the convection section for stripping.

The invention provides a device for preparing low-carbon olefin by cracking crude oil, which comprises a cracking furnace, a hydrogenation reactor and at least two groups of cyclone separators, wherein a convection section of the cracking furnace comprises a convection section first pipe group and a convection section second pipe group, the convection section first pipe group is connected with an inlet of the first cyclone separator, a liquid phase outlet of the first cyclone separator and the hydrogenation reactor in a closed loop manner, the convection section first pipe group is connected with an inlet of the second cyclone separator, and a vapor phase outlet of the second cyclone separator is connected with a vapor phase outlet of the first cyclone separator and the convection section second pipe group.

In the invention, the preheated crude oil is subjected to gas-liquid separation by adopting the cyclone separator, the cyclone separator has the advantages of simple structure, small volume, light weight, low cost, high separation efficiency and convenient installation and operation, can overcome the defects of a flash evaporator, is particularly suitable for the reconstruction of the conventional cracking furnace device, and realizes the separation of the preheated crude oil in a narrow space; in addition, the method also comprises the step of hydroprocessing, and the combination of processes such as mixing liquid hydrocarbon with the hydroprocessed material is adopted, so that the crude oil cracking efficiency is effectively improved, the yield of olefin products is increased, the coking and blockage of the cracking furnace in the radiation section and the quenching part are reduced, and the operation cost is reduced.

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

Detailed Description

The following describes in detail specific embodiments of the present invention. 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.

According to a first aspect of the present invention, the present invention provides a method for preparing low carbon olefins by cracking crude oil, comprising the following steps:

In the invention, the stripped second liquid phase can be used as heavy fuel oil.

According to the invention, the process also comprises at least one addition of steam and/or hydrogen, which can be arranged in any step before the introduction into the radiant section, which, when arranged in step 2), should be carried out after the hydroprocessing. The addition of steam and/or hydrogen reduces the hydrocarbon partial pressure of the cracking raw material, and is beneficial to the generation of low-carbon olefin.

The steam may be sour process steam or deacidified process steam. The steam may be heated by any means known in the art, and is preferably superheated in the convection section of the furnace.

In the present invention, the hydroprocessing of the first liquid phase may be at least one of hydrotreating, hydrogenation, and hydrocracking, preferably hydrotreating.

In the invention, the liquid hydrocarbon is added into the first liquid phase after hydroprocessing so as to ensure that the cracking furnace has higher furnace tube outlet temperature (COT) than the original furnace tube and improve the yield of the low-carbon olefin in the product. Preferably, the liquid hydrocarbon has a boiling point of 37 to 565 ℃. Specific examples of the liquid hydrocarbon include, but are not limited to: light straight run naphtha, kerosene, heavy atmospheric tail oil, hydrogenated tail oil, hydrocracking products and the like.

According to the invention, the weight percentage of the hydroprocessed first liquid phase in the mixture (i.e. the mixture of hydroprocessed first liquid phase and liquid hydrocarbons) may be between 1 and 99%, preferably between 20 and 95%.

According to the invention, the outflow temperature of the preheated crude oil is 315-565 ℃, and the pressure is 0.1-1.5 MPa.

In the present invention, the preheated crude oil is transferred to the first cyclone to be subjected to gas-liquid separation, and the liquid phase volume content of the preheated crude oil at the inlet of the first cyclone is preferably 0.01 to 5%, more preferably 0.02 to 2%.

According to the invention, the outflow temperature of the preheated mixture is 315-565 ℃ and the pressure is 0.1-1.5 MPa.

In the present invention, the preheated mixture is fed to the second cyclone to be subjected to gas-liquid separation, and the liquid phase volume content of the preheated mixture at the inlet of the second cyclone is preferably 0.01 to 5%, more preferably 0.02 to 2%.

In the present invention, the "cyclone" refers to a cyclone in a broad sense, and includes both a "cyclone" in a narrow sense and a separation device similar to the principle thereof in the art, such as a cyclone. Unless otherwise specified, the cyclone separators mentioned in the present invention are all cyclone separators in a broad sense.

According to the invention, most of working media of the first cyclone separator and the second cyclone separator for gas-liquid separation are gas, and the cyclone separator which is conventionally used in the field can be selected as long as the separation of high-concentration and high-viscosity liquid at high temperature can be realized, and the separation efficiency can reach more than 90%.

Specific examples of the first cyclone and the second cyclone include, but are not limited to: the cyclone separator comprises a rectangular inlet cyclone separator, a volute type cyclone separator, an axial flow guide vane type cyclone separator, a straight cylinder type cyclone separator, a cone cylinder combined type cyclone separator, a counter-flow type cyclone separator, a straight-flow type multi-cyclone pipe separator and the like. The first cyclone and the second cyclone may be the same or different. Preferably, the first cyclone separator and the second cyclone separator are each selected from a spiral shell type cyclone separator, an axial flow guide vane type cyclone separator, a straight tube type cyclone separator, a cone and cylinder combination type cyclone separator, or a straight flow type cyclone separator.

The crude oil or mixture preheated by the first tube group of the convection section of the cracking furnace has the characteristics of high temperature, high liquid content and high liquid viscosity. For such gas-liquid mixture, in order to ensure the separation efficiency of the cyclone separator, the first cyclone separator and the second cyclone separator in the invention are preferably provided with cyclone separators with internal components, such as a top skimming cylinder is added in the cyclone separator to reduce the loss of liquid films on the wall surface of the upper part of the cyclone separator, and a separation plate and a vortex breaker can be simultaneously or not simultaneously added at the lower part of the cyclone separator to reduce the entrainment of the tail part of gas vortex to the liquid at the lower part of the cyclone separator and the liquid on the wall surface.

In the invention, the number of the cyclone separators can be selected according to requirements, and the first cyclone separator and the second cyclone separator can comprise one or more cyclone separators. When a plurality of cyclone separators are included, the plurality of cyclone separators may be connected in parallel or in series.

In the present invention, the content of the liquid phase in the first vapor phase and the second vapor phase is less than 10g/m³Preferably less than 200mg/m³。

The cracking furnace adopted by the invention can be a cracking furnace for preparing low-carbon olefin by steam cracking which is conventionally used in the field. Preferably, the cracking furnace used is a tubular cracking furnace. Cracking furnaces typically include primarily a convection section, a radiant section, a quench section, and a gas fired system. In a cracking furnace, crude oil is sent into a first tube group of a convection section (the convection section comprises the first tube group of the convection section and a second tube group of the convection section), the crude oil is contacted with superheated steam for preheating (315-, the cracked gas enters a quenching part after coming out of the radiation section, so that the low-carbon olefin is obtained.

The cracking furnace used in the present invention and the method for obtaining low carbon olefins from the cracking furnace are well known to those skilled in the art and will not be described herein.

According to a second aspect of the invention, the invention provides a device for preparing low-carbon olefins by cracking crude oil, which comprises a cracking furnace, a hydrogenation reactor and at least two sets of cyclones, wherein a convection section of the cracking furnace comprises a convection section first tube group and a convection section second tube group, the convection section first tube group is connected with an inlet of the first cyclone, a liquid phase outlet of the first cyclone and the hydrogenation reactor in a closed loop manner, the convection section first tube group is connected with an inlet of the second cyclone, and a vapor phase outlet of the second cyclone is connected with a vapor phase outlet of the first cyclone and the convection section second tube group.

The cyclone separators (the first cyclone separator and the second cyclone separator) and the cracking furnace used in the device for preparing low-carbon olefins by cracking crude oil are as described above, and are not described herein again.

In addition, the hydrogenation reactor in the present invention may be conventionally selected according to the manner of hydroprocessing.

The present invention will be described in detail below with reference to examples.

The compositions of the crude oils used in the following examples and comparative examples, which were measured according to the method of ASTM D5307, are shown in table 1 below.

TABLE 1

Analysis item	ASTM D5307
		IP，℃	69
10％，℃	192
		20％，℃	272
30％，℃	337
		40％，℃	393
50％，℃	446
		60％，℃	508
70％，℃	595
		75％，℃	653
80％，℃	-
		90％，℃	-
EP，℃	-

Example 1

This example illustrates the process of the present invention for the preparation of lower olefins by cracking crude oil.

The method specifically comprises the following steps:

1. the dehydrated and desalted crude oil is directly sent into a CBL-III type cracking furnace (purchased from China petrochemical industry group company), and is preheated in a first pipe group at a convection section, wherein the temperature of the preheated crude oil is 380 ℃, and the pressure is 0.15 MPa. And (3) sending the preheated crude oil into a volute type cyclone separator (a first cyclone separator) provided with a separation plate and an internal component of a vortex breaker, and carrying out gas-liquid separation. The inlet liquid phase content of the volute type cyclone separator is 0.04% (V/V), and the liquid phase density is 800kg/m³Gas phase density of 0.85kg/m³. The separation efficiency of the volute type cyclone separator is 98 percent, and the liquid phase in the vapor phase after separation is 200mg/m³。

2. The separated liquid phase is subjected to hydrogenation treatment by adopting Co-Ni-Mo/Al as a catalyst₂O₃The hydrogenation temperature is 270 ℃, the hydrogenation pressure is 2.6MPa, the hydrogen-oil ratio is 3.0, and the volume space velocity of crude oil is 2.0h^-1The hydrogenation rate of monoene is 95%. The hydrotreated stream was mixed with naphtha to produce a mixture wherein the mass ratio of hydrotreated stream to naphtha was 90: 10.

3. The mixture was also fed into a CBL-III type cracking furnace (from China petrochemical industry group) and preheated in the first tube bank at a convection section at a temperature of 380 ℃ and a pressure of 0.15 MPa. The preheated mixture was fed to a guide vane cyclone separator (second) provided with a top skimmer drum, a partition plate and a vortex breaker inner memberCyclone), gas-liquid separation is performed. The inlet liquid phase content of the guide vane type cyclone separator is 0.03 percent (V/V), and the liquid phase density is 800kg/m³Gas phase density of 0.80kg/m³. The separation efficiency of the guide vane type cyclone separator is 98%, and the liquid phase in the separated vapor phase is 200mg/m³。

4. Sending the vapor phase separated in the step 3 and the vapor phase separated in the step 1 into a second tube group of a convection section of the CBL-III steam cracking furnace, heating to a cross temperature (510 ℃), then sending into a radiation section, and cracking to generate cracking gas containing olefin; the operation parameters of the radiation section are that the water-oil ratio is 0.75, the outlet temperature of the furnace tube is 840 ℃, and the retention time is 0.21 s. The product had an ethylene yield of 23.54 wt%, a propylene yield of 12.27 wt%, a 1, 3-butadiene yield of 4.42 wt%, and a triene yield of 40.22 wt%. And (3) contacting the liquid phase separated in the step (3) with superheated steam in a convection section, and performing steam stripping to obtain the heavy fuel oil.

Comparative example 1

The steam cracking reaction was carried out according to the method of example 1, except that the dehydrated and desalted crude oil was directly fed into a CBL-III type cracking furnace, passed through a convection section, and then directly fed into a radiation section for cracking. The pyrolysis gas adopts a sequential separation process of LUMMUS. Analysis of the steam cracking reaction product revealed that the yield of ethylene was 21.49 wt%, the yield of propylene was 13.29 wt%, the yield of 1, 3-butadiene was 4.03 wt%, and the yield of triene was 38.81 wt%.

Comparative example 2

The steam cracking reaction is carried out according to the method of the embodiment 1, and the difference lies in that crude oil preheated by the first tube group of the convection section of the cracking furnace is sent into the first flash tank for gas-liquid separation, the separation efficiency is 90%, then the separated gas phase returns to the second tube group of the convection section of the cracking furnace, enters the radiation section for cracking after being continuously preheated, the liquid phase product separated by the first flash tank is continuously hydrotreated, then is mixed with naphtha, enters the second flash tank for gas-liquid separation after being preheated by the first tube group of the convection section of the cracking furnace, the separation efficiency is 90%, then the gas phase returns to the cracking furnace for continuous preheating, enters the radiation section for cracking, and the cracking gas adopts the sequential separation flow of LUMMUS. Analysis of the steam cracking reaction product revealed that the yield of ethylene was 23.36% by weight, the yield of propylene was 12.32% by weight, the yield of 1, 3-butadiene was 4.37% by weight, and the yield of triene was 40.05% by weight.

The comparison shows that the method for preparing the low-carbon olefin by cracking the crude oil can obviously improve the yield of the low-carbon olefin. Specifically, comparing example 1 with comparative example 1, the crude oil in comparative example 1 is directly subjected to a steam cracking reaction, while the crude oil in example 1 is subjected to gas-liquid separation, hydroprocessing, mixing with liquid hydrocarbons, and the like, through two cyclones. It is evident from the cracking results that example 1 gives a significantly higher yield of lower olefins. Example 1 was compared with comparative example 2, in which gas-liquid separation was performed using a flash tank, and in example 1, gas-liquid separation was performed using a cyclone. From the cracking results, it is seen that example 1 achieves a higher yield of lower olefins.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing low-carbon olefin by cracking crude oil is characterized by comprising the following steps:

2. The method of claim 1, further comprising the step of adding steam and/or hydrogen at least once.

3. A method according to claim 2, wherein the added steam is sour process steam or deacidified process steam.

4. The method of claim 3, wherein the added steam is superheated in a convection section of the pyrolysis furnace.

5. The method of claim 1, wherein the hydroprocessing comprises hydrotreating.

6. The method of claim 1, wherein the hydroprocessing comprises hydrogenation.

7. The method of claim 1, wherein the hydroprocessing comprises hydrocracking.

8. The method of claim 1, wherein the liquid hydrocarbon has a boiling point of 37-565 ℃.

9. The process of claim 8, wherein the liquid hydrocarbon is at least one of light virgin naphtha, kerosene, heavy atmospheric tail oil, hydrogenated tail oil, and hydrocrackate.

10. The method of claim 1, wherein the mixture comprises 1-99% by weight of the first liquid phase after hydroprocessing.

11. The method of claim 10, wherein the weight percentage of the hydroprocessed first liquid phase in the mixture is 20-95%.

12. The method as claimed in claim 1, wherein the preheated crude oil has an outflow temperature of 315 ℃ and an outflow temperature of 565 ℃ and a pressure of 0.1 to 1.5 MPa; the liquid phase volume content of the preheated crude oil at the inlet of the first cyclone separator is 0.01-5%.

13. The method as claimed in claim 12, wherein the preheated crude oil has a liquid phase volume content of 0.02-2% at the inlet of the first cyclone.

14. The method as claimed in claim 1, wherein the outflow temperature of the preheated mixture is 315-565 ℃, and the pressure is 0.1-1.5 MPa; the preheated mixture has a liquid phase volume content of 0.01-5% at the inlet of the second cyclone.

15. The process as claimed in claim 14, wherein the preheated mixture has a liquid phase volume content of 0.02-2% at the inlet of the second cyclone.

16. The method of claim 1, wherein the first and second cyclones are each selected from the group consisting of a scroll type cyclone separator, an axial flow guide vane type cyclone separator, a straight type cyclone separator, a cone and cylinder combination type cyclone separator, and a straight type cyclone separator.

17. The method of claim 16, wherein the first and second cyclones are provided with internals comprising skimmers at the top of the cyclones and/or baffles, vortex breakers at the lower part of the cyclones.

18. The method of claim 1, wherein the first stepThe content of liquid phase in the first vapor phase and the second vapor phase is less than 10g/m³。

19. The method of claim 18, wherein the liquid phase content in the first and second vapor phases is less than 200mg/m³。

20. An apparatus for preparing low carbon olefin by cracking crude oil, which is used in the method of any one of claims 1 to 19, and comprises a cracking furnace, a hydrogenation reactor and at least two sets of cyclones, wherein the convection section of the cracking furnace comprises a convection section first tube bank and a convection section second tube bank, the convection section first tube bank is connected with an inlet of the first cyclone, a liquid phase outlet of the first cyclone and the hydrogenation reactor in a closed loop manner, the convection section first tube bank is connected with an inlet of the second cyclone, and a vapor phase outlet of the second cyclone is connected with a vapor phase outlet of the first cyclone and the convection section second tube bank.