CN116004271A

CN116004271A - Steam cracking process and system

Info

Publication number: CN116004271A
Application number: CN202111234820.3A
Authority: CN
Inventors: 李蔚; 石莹; 周丛; 张利军; 王国清; 张兆斌; 蒋冰
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: 2021-10-22
Filing date: 2021-10-22
Publication date: 2023-04-25

Abstract

The invention relates to the field of preparing low-carbon olefin from crude oil, and discloses a steam cracking method and a steam cracking system of crude oil. The method is carried out in a pyrolysis furnace comprising a convection section and a radiant section, the method comprising: mixing and heating crude oil with steam in a convection section under a reduced pressure condition until the crude oil crosses the temperature, and then entering a radiation section for steam cracking reaction to obtain low-carbon olefin; wherein the cross temperature is 350-500 ℃. By adopting the method, the coking phenomenon in the convection section furnace tube of the cracking furnace can be reduced, the burning period of the radiant section is prolonged, the device online rate is improved, the cracking efficiency of crude oil is improved, and the product yield is improved.

Description

Steam cracking process and system

Technical Field

The invention relates to the field of preparation of low-carbon olefins, and discloses a steam cracking method and a steam cracking system.

Background

In order to fully utilize crude oil resources and improve the yield of low-carbon olefins, various hydrocarbon raw materials are usually cracked into olefins by steam cracking in a cracking furnace. A common pyrolysis furnace includes a convection section and a radiant section. Crude oil is generally divided into four components, saturated, aromatic, colloidal and asphaltene, where saturated and asphaltene represent the most stable and least stable components of crude oil, respectively. The crude oil contains high molecular weight non-volatile components with boiling point exceeding 590 ℃, and when the non-volatile components are preheated in the convection section of a conventional cracking furnace, a small part of the non-volatile components are not gasified, and the non-volatile components which are not gasified are clamped to the radiation section along with the mixed airflow, so that coking deposition of the radiation section is easily caused, even the radiation section is blocked, the online rate of a cracking device is influenced, and the product yield is influenced.

CN101583697a discloses a process for cracking a feedstock comprising synthetic oil, the process comprising: 1. hydroprocessing includes a broad boiling range aliquot of: a normally liquid hydrocarbon portion boiling in the range of 50°f to 800°f that is substantially free of resid, and b a thermally cracked hydrocarbon liquid boiling in the range of 600°f to 1050°f to provide a synthetic crude oil boiling in the range of 73°f to 1070°f that comprises greater than 25wt% aromatics, greater than 25wt% naphthenes, less than 0.3wt% S, less than 0.02wt% asphaltenes, and substantially free of resids other than asphaltenes; 2. adding to the synthetic crude a normally liquid hydrocarbon component boiling in the range of 100 DEG F to 1050 DEG F; and 3, cracking the mixture produced by 2 in a cracking furnace to provide a cracked effluent, wherein the cracking furnace includes a radiant coil outlet, wherein the cracking is conducted under conditions sufficient to obtain a radiant coil outlet temperature greater than the optimum for cracking the synthetic crude oil alone.

The method mixes the crude oil with the existing ethylene production raw material, dilutes the crude oil, improves the cracking performance of the crude oil, and improves the conversion rate of olefins. However, the method is limited by the source of the existing ethylene production raw materials, and can not effectively utilize a large amount of crude oil to produce low-carbon olefin.

In addition to improvements in the process to reduce the impact of crude oil, such as crude oil, on the cracking furnace tubes, improvements in the design of the cracking furnace tubes are contemplated. As known by those skilled in the art, the radiant section furnace tube of the cracking furnace has the characteristics of high temperature, short residence time, low hydrocarbon partial pressure and the like, and is beneficial to high selectivity, high capacity and long-period operation of ethylene production. The cracking furnace has the technical patent that two-pass branch reducing furnace tubes or two-pass reducing furnace tubes with high selectivity are adopted, the first pass adopts a small-diameter furnace tube, the aim of rapid temperature rise is achieved by utilizing the characteristic of large specific surface area, and the second pass adopts a large-diameter furnace tube, so that coking sensitivity in the later stage of hydrocarbon cracking reaction is reduced. At present, two-pass high-selectivity radiation furnace tubes for industrial application mainly comprise a type 2-1 type, a type 4-1 type, a type 5-1 type, a type 6-1 type, a type 8-1 type and a type U (1-1), and the high-selectivity furnace tube has large specific surface area and high heating speed, thereby being very beneficial to hydrocarbon cracking reaction.

CN101333147a proposes an ethylene cracking furnace, in which furnace tubes are located in a radiant section, each furnace tube is composed of an inlet tube and an outlet tube, the furnace tubes are arranged in two rows in the radiant section, each row forms a plane of a tube row, the inlet tube and the outlet tube of the furnace tube are located in two different planes of the tube row respectively in an alternate interval form, and are connected together at the bottom by a symmetrical U-shaped connector. The cracking furnace is considered to be large in size, the radiant heat transfer efficiency is improved by the arrangement mode of the furnace tubes, the operation period is prolonged, and the energy consumption of products is reduced.

CN103992812a describes a cracking furnace, in which four rows of burners and two groups of radiant tubes are arranged at the bottom of the radiant section, and each group of radiant tubes is arranged in two rows, so that four rows of radiant tubes are provided in total in the radiant section, which is considered to realize the large-scale of the cracking furnace and reduce the occupation and investment.

CN103992813a describes an ethylene cracking furnace comprising a radiant section, a convection section, a quench heat exchanger, and an induced draft fan and chimney, wherein two rows of radiant tubes are provided in the radiant section, including an inlet tube row formed by a row of inlet tubes and an outlet tube row formed by a row of outlet tubes, a plurality of burners are arranged on both sides of the two rows of radiant tubes, the burners being arranged to be able to asymmetrically supply heat to the radiant tubes such that the heat release of the burners near the inlet tube row is greater than the heat release of the burners near the outlet tube row. It is considered that the cracking furnace has long operation period, high product yield and large production capacity.

CN104232146a discloses an ethylene cracking furnace, which comprises a radiant section coil pipe assembly, the assembly is composed of X-type radiant coil pipe modules which are arranged in the radiant section along the length direction of the furnace body and perpendicular to the bottom surface, each X-type radiant coil pipe module is composed of four groups of radiant coil pipes, and each group of radiant coil pipes is composed of furnace pipes. The four groups of radiant coils are connected with four-in-one stereoscopic polymeric pipes at the center of the X-type radiant coil module to serve as material outlets, the farthest gate of the four groups of radiant coils, which is far away from the center of the X-type radiant coil module, serves as a material inlet and is connected with an inlet collecting pipe together, and the bottom burner is arranged at a gap between every two adjacent radiant coils. It is considered that each furnace tube on each independent radiant coil is heated uniformly, so that the service life of the furnace tube is prolonged and the ethylene production capacity is improved.

The focus of the above patent is focused on how the furnace tubes in the radiant section of the cracking furnace are arranged to ensure more arrangement of the furnace tubes in the furnace chamber and better radiant heat transfer, so that the materials in the furnace tubes can be quickly heated in a very short residence time, but are not suitable for cracking crude oil. Because crude oil (such as crude oil) is used directly as a cracking feedstock, it is often insufficiently gasified and has the characteristic of being easily coked, resulting in low yields of low olefins, which is also an important reason why it has not been used as a cracking feedstock before. Moreover, coking occurs in a convection section of the cracking furnace, namely a relatively low-temperature area, once the convection section is coked, the coking cannot be removed by an on-line coking means, and the furnace is usually stopped for manual coke cleaning, so that the on-line time of the cracking furnace is greatly influenced.

Disclosure of Invention

The invention aims to solve the problems of insufficient gasification, convection Duan Yi coking, low yield of low-carbon olefin and the like in the prior art when crude oil is used for cracking and producing low-carbon olefin, and provides a steam cracking method and a steam cracking system.

In order to achieve the above object, a first aspect of the present invention provides a steam cracking method implemented in a cracking furnace including a convection section and a radiant section, the method comprising:

under the condition of decompression, the pyrolysis raw material is mixed with water vapor in a convection section and heated to cross temperature, and then enters a radiation section for steam pyrolysis reaction to obtain low-carbon olefin;

wherein the cross temperature is 350-500 ℃.

In a second aspect, the present invention provides a steam cracking system, the system comprising:

a pyrolysis furnace comprising a convection section and a radiant section connected in series; and

the material inlet of the pressure reducing device is connected with the material outlet of the radiation section of the cracking furnace and is used for providing pressure reducing conditions;

wherein the convection section is used for contacting the pyrolysis raw material with steam and heating to a crossing temperature, and the number of the convection section furnace tubes can enable the crossing temperature to be 350-500 ℃.

By adopting the method, the pyrolysis raw material is gasified and steam cracked under the reduced pressure state, the cross temperature is controlled within the range of 350-500 ℃, the normal running of the pyrolysis reaction of the radiant section is kept, the coking phenomenon in the pyrolysis furnace tube, particularly the convection furnace tube, can be reduced, the furnace shutdown treatment step required by the decoking of the convection section is avoided, and the burning period of the radiant section is prolonged; meanwhile, the operation is carried out under the condition of decompression, so that the operation period of the cracking furnace is further prolonged, and the online rate of the device is improved.

Drawings

FIG. 1 is a schematic view of a steam cracking system according to the present invention.

Description of the reference numerals

1. A convection section; 2. a radiation section; 3. a pyrolysis furnace; 4. quenching the boiler; 5. a separation tower; 6. a reflux condenser; 7. a pressure reducing device; 8. a pressure reducing device.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

In a first aspect the present invention provides a steam cracking process carried out in a cracking furnace comprising a convection section and a radiant section, the process comprising:

wherein the cross temperature is 350-500 ℃.

In the present invention, the cross-over temperature may be, for example, 350, 360, 380, 400, 420, 430, 435, 440, 445, 450, 455, 460, 465, 470, 475, 480, 490, 500 ℃ and any range between any two values; preferably, the cross-over temperature is 430-480 ℃.

This can be achieved by reducing the number of rows of hybrid heating section tubes in the convection section and adjusting the set temperature.

In the present invention, the pyrolysis feedstock is a pyrolysis feedstock in the conventional sense in the art, and specifically, the pyrolysis feedstock may include light naphtha, diesel, hydrogenated tail oil, light crude oil, crude oil having a final boiling point of above 600 ℃ and below 700 ℃ and dehydrated and desalted crude oil.

Preferably, the cracking raw material is at least one selected from diesel oil, hydrogenated tail oil, light crude oil, dehydrated and desalted crude oil and crude oil with a final boiling point higher than 600 ℃ and lower than 700 ℃.

Preferably, the cracking feedstock has an API greater than 18, more preferably greater than 22, such as may be 24, 26, 28, 30, 32, 34, 36, 38, 40 or more and any range between any two values.

API gravity is a measure developed by the American Petroleum Institute (API) to represent the density of petroleum and petroleum products. The API gravity can be obtained by measuring the density of the raw material and then converting the raw material.

In the present invention, the low-carbon olefin means an olefin having a relatively small number of carbon atoms, for example, an olefin having 4 or less carbon atoms.

In order to make full use of the heat of the high temperature flue gas from the radiant section, the convection section of the pyrolysis furnace is typically provided with a plurality of sections for recovering heat. Typically, the convection section may be provided with a feed preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a hybrid heating section. The feedstock preheating stage is typically used to preheat the pyrolysis feedstock. The boiler feed water preheating section is typically used to preheat the boiler feed water supplied to the drum. The dilution steam superheating section is typically used to preheat dilution steam (e.g., steam). The super-high pressure steam superheating section is typically used to heat high pressure steam from a drum to obtain super-high pressure steam. The hybrid heating stage is typically used to heat the pyrolysis feedstock to a cross-over temperature. In the preferred embodiment, in the convection section, a mixed heating section, an ultrahigh pressure steam superheating section, a dilution steam superheating section, a boiler feed water preheating section, and a raw material preheating section are preferably provided in this order along the flow direction of the high-temperature flue gas.

Preferably, the method further comprises: before mixing steam with the pyrolysis raw material, preheating the pyrolysis raw material in a convection section to obtain a preheated raw material.

Preferably, the temperature of the preheated feedstock is 120-300 ℃, more preferably 150-250 ℃.

The convection section preferably comprises a first tube group of the convection section (comprising a raw material preheating section, a boiler feed water preheating section, a dilution steam superheating section, an ultrahigh pressure steam superheating section and a mixed heating section) and a second tube group of the convection section (comprising a mixed heating section). The crude oil is fully gasified in the first tube group of the convection section, so that the steam cracking effect is effectively improved.

Preferably, the temperature of the water vapour is 480-560 ℃, preferably 500-540 ℃.

Preferably, the weight ratio of the crude oil to the water vapor is 1-4:1, more preferably 1.5-2.5:1.

the cleavage of the material to a cross-over temperature is carried out in the radiant section, preferably the cleavage reaction conditions include: the outlet temperature of the radiation section is 780-850 ℃, preferably 790-840 ℃.

In the present invention, the radiant section comprises a multi-pass furnace, preferably a 2-6 pass furnace, more preferably a two pass furnace.

The two-pass furnace tube can be, for example, two parallel vertical inlet tubes in the first pass and one vertical outlet tube in the second pass to form a 2-1 type radiation furnace tube; or the first pass is four parallel vertical inlet pipes, and the second pass is a vertical outlet pipe, so that a 4-1 type radiation furnace tube is formed.

Preferably, the ratio of the inner diameter of the outlet tube to the inner diameter of the inlet tube of the multi-pass furnace tube is in the range of: more than 1 and less than or equal to 2.5.

In a preferred embodiment of the present invention, the inlet tube inner diameter of the multi-pass furnace tube ranges from 25mm to 70mm, more preferably from 40mm to 65mm.

In a preferred embodiment of the present invention, the inner diameter of the outlet tube of the multi-pass furnace tube ranges from 45mm to 120mm, more preferably from 60mm to 95mm.

The radiation section furnace tube can also adopt an enhanced heat transfer element, and the enhanced heat transfer element can be various known or unknown elements, such as a spiral sheet insert, a twisted belt insert, a crossed zigzag insert, a coil core insert, a filament winding porous body, a spherical substrate insert and the like, so as to facilitate heat transfer. Different reinforced heat transfer elements can also be respectively added in different parts of the furnace tube.

In order to further increase the cracking efficiency of petroleum hydrocarbons while increasing the yield of lower olefins in the product, the pressure of the depressurization condition is preferably 0.5kPa to 101kPa absolute pressure, preferably 1kPa to 10kPa. The depressurization may be achieved by a depressurization device conventional in the art.

In the invention, the absolute pressure of the cracking furnace is in the range, so that the cracking efficiency of the petroleum hydrocarbon can be further effectively improved, the gasification effect of the petroleum hydrocarbon can be further improved, and the coking of the petroleum hydrocarbon in the radiation section of the cracking furnace is reduced.

In the present invention, the pyrolysis furnace may be used in conjunction with other conventional equipment to effect steam pyrolysis, such as may be provided with a quench device, drum, fan, and pyrolysis gas header.

The material obtained after the pyrolysis in the radiation section can be cooled in a quenching device and separated into pyrolysis gas and steam. The separated steam enters a steam drum to carry out gas-liquid separation, the separated high-pressure steam can enter a convection section to be heated so as to obtain ultrahigh-pressure steam, and the separated water can be used as cooling water of a quenching heat exchanger; the pyrolysis gas enters a subsequent separation device through a pyrolysis gas main pipe to separate out a desired target product. High-temperature flue gas generated by combustion in the radiation section enters the convection section through the flue gas crossing section.

The quench device may be a quench device conventional in the art, such as a quench heat exchanger.

In the present invention, unless otherwise specified, the methods and apparatus involved are conventional in the art.

In a second aspect, the present invention provides a steam cracking system for crude oil, the system comprising:

wherein the convection section is used for contacting crude oil with steam and heating to a crossing temperature, and the number of convection section furnace tubes can enable the crossing temperature to be 350-500 ℃.

The convection section may include at least one tube bank, such as may be two tube banks.

Preferably, the pressure reduction device comprises a separation column, a reflux condenser and a pressure reduction apparatus connected in series; wherein, the separation tower is communicated with the cracking furnace.

The specific structure of each device is described in the first aspect, and will not be described herein. The devices used, without specific description, all have a structure conventional in the art.

It will be appreciated that other ancillary facilities may be provided in the system, such as a quench device, for cooling the cracked material from the radiant section and separating the lower olefins.

Preferably, the material inlet of the quenching device is connected with the material outlet of the radiation section, and the material outlet of the quenching device is connected with the material inlet of the decompression device.

The present invention will be described in detail by examples.

In the following examples, the cracking feedstock used was dehydrated desalted crude oil having a density of 862.4kg/m at 20 ℃ ³ The API level is about 33.

The cracking furnace used in the following examples was modified based on a CBL-III type cracking furnace purchased from chinese petrochemical company, in which two sets of mixed heating section tube banks were reduced as the cracking furnace used in example 1.

Example 1

This example is intended to illustrate a steam cracking process for crude oil.

The steam cracking system shown in FIG. 1 was used for the cracking reaction. The system comprises a cracking furnace 3, a quenching boiler 4 and a decompression device 8 which are connected in series, wherein the cracking furnace 3 comprises a convection section 1 and a radiation section 2 which are connected in series; the pressure reducing device 8 comprises a separating tower 5, a reflux condenser 6 and a pressure reducing device 7 which are connected in series; the material outlet of the radiation section 2 is connected with the material inlet of the quenching boiler 4, and the material outlet of the quenching boiler 4 is connected with the material inlet of the separation tower 5. The convection section 1 (comprising a first tube group of the convection section and a second tube group of the convection section) of the cracking furnace 4 comprises a raw material preheating section, a boiler feed water preheating section, a dilution steam superheating section, an ultrahigh pressure steam superheating section and a mixed heating section. The raw material preheating section is used for preheating crude oil; the boiler feed water preheating section is used for preheating boiler feed water supplied into the steam drum; the dilution steam superheating section is used for preheating dilution steam (such as water vapor); the ultrahigh pressure steam superheating section is used for heating high pressure steam from the steam drum to obtain ultrahigh pressure steam; the hybrid heating section is used to heat the crude oil to a cross-over temperature.

The steam cracking method comprises the following steps: the crude oil with the temperature of 60 ℃ is gasified and preheated in the convection section 1, heated to the cross temperature (XOT) of 450 ℃, and then enters a furnace tube of the radiation section 2 for cracking reaction. Wherein the crude oil is 47000kg/h and the dilution steam is 37600kg/h. The cracking reaction product is sent to a quenching boiler 5 for cooling separation. In the steam cracking process, a pressure reducing device is started to ensure that the absolute pressure in the system is reduced to 5kPa, and the absolute pressure of crude oil in a cracking furnace 3 is 5kPa. The radiant section inlet pressure XOP of the pyrolysis furnace was 0.009MPaG, the radiant section outlet temperature (COT) was 790 ℃, and the radiant section outlet pressure COP was 0.005MPaG. The radiant section furnace tube 3 adopts a two-pass furnace tube, the inlet tube diameter of the furnace tube is 51mm, the outlet tube diameter of the furnace tube is 73mm, and the tube length of the furnace tube is 26.6m.

Example 1 reduced the heat exchange tube banks of the hybrid heating section in the convection section, reduced the cross-over temperature of the feed compared to comparative example 1 (520 ℃) by reducing the heat exchange of the feed, steam mixture with the flue gas in the hybrid heating section, which effectively reduced the cracking reaction in the convection section, and reduced coking. Operating according to example 1, the cracking furnace was operated for a period of 70 days, 5 times of on-line coking in one year, each time of 2 days; the main composition of the cleavage product is shown in Table 1.

Comparative example 1

This comparative example is used to illustrate the steam cracking process of the reference.

The pyrolysis was carried out in a steam cracking system consisting of a CBL-III type pyrolysis furnace and a quenching boiler connected in series therewith, i.e., unlike example 1, the system did not contain a depressurizing device, and the number of tube rows of the mixed heating section in the convection section of the pyrolysis furnace was two more.

The procedure of example 1 was followed, except that the crossover temperature was 520 ℃.

The running period of the cracking furnace is 65 days, the convection section is decoked once (7 days, and the furnace is additionally stopped and opened once) within one year, the on-line coke is burnt for 5 times, and the time for each coke burning is 2 days; the main composition of the cleavage product is shown in Table 1.

TABLE 1

The yield of the main product is wt%	Example 1	Comparative example 1
			Ethylene	25.05	23.01
Propylene	13.45	13.02
			Butadiene	5.76	5.05

It can be seen that the on-line time of the cracking furnace was increased by 12 days in one year, and a large amount of products were increased, and only triene (ethylene, propylene, butadiene) products were increased by 12818 tons, as compared with comparative example 1 in example 1. For example, according to the unit price of 7000 yuan Renzhen/ton (since the price of the product is changed, a conventional fixed value is taken here for the convenience of calculation), only the triene product is increased to 8972 yuan Renzhen. In addition, the example saves a lot of costs for starting and stopping and maintaining compared with comparative example 1.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A steam cracking process, wherein the process is carried out in a cracking furnace, said furnace comprising a convection section and a radiant section, the process comprising:

wherein the cross temperature is 350-500 ℃.

2. The method of claim 1, wherein the cross-over temperature is 430-480 ℃.

3. The process according to claim 1, wherein the cracking feedstock has an API gravity of 18 or more, preferably 22 or more;

preferably, the cracking feedstock is selected from at least one of light naphtha, diesel, hydrogenated tail oil, light crude oil, crude oil with a final distillation point higher than 600 ℃ and lower than 700 ℃ and dehydrated desalted crude oil, more preferably diesel, hydrogenated tail oil, light crude oil, dehydrated desalted crude oil and crude oil with a final distillation point higher than 600 ℃ and lower than 700 ℃.

4. The method of claim 1, wherein the method further comprises: preheating the pyrolysis raw material in a convection section under reduced pressure before mixing water vapor with the pyrolysis raw material to obtain a preheated raw material;

5. A process according to claim 1, wherein the temperature of the water vapour is 480-560 ℃, preferably 500-540 ℃.

6. The process according to any one of claims 1 to 5, wherein the weight ratio of the amount of cracking feedstock to water vapor is 1 to 4:1, preferably 1.5-2.5:1.

7. a process according to claim 1, wherein the pressure of the reduced pressure conditions is 0.5kPa to 101kPa absolute, preferably 1kPa to 10kPa absolute.

8. The method of any one of claims 1-7, wherein the cleavage reaction conditions comprise: the outlet temperature of the radiation section is 780-850 ℃, preferably 790-840 ℃.

9. The method of claim 1, wherein the method further comprises: and separating the cracked product to obtain the low-carbon olefin.

10. A steam cracking system, the system comprising:

11. The system of claim 10, wherein the pressure reduction device comprises a separation column, a reflux condenser, and a pressure reduction apparatus connected in series; wherein, the separation tower is communicated with the cracking furnace.