Cracking furnace, steam cracking system and method

Abstract

This invention relates to the field of crude oil to low-carbon olefins, and discloses a cracking furnace, a steam cracking system, and a method. The method is implemented in a cracking furnace, which includes a convection section and a radiant section. The method includes: mixing and heating the cracking feedstock with steam in the convection section to a transverse temperature, and then introducing it into the radiant section for steam cracking to obtain low-carbon olefins; wherein the inner surface of the furnace tubes in the convection section undergoes surface modification treatment to reduce coking within the furnace tubes; and wherein the transverse temperature is 350-500°C. Using this method, coking in the furnace tubes of the convection section of the cracking furnace can be reduced, the coking cycle in the radiant section can be extended, the online rate of the unit can be improved, the cracking efficiency of crude oil can be increased, and product yield can be increased.

Description

Technical Field

[0001] This invention relates to the field of preparing low-carbon olefins, and discloses a steam cracking method, a cracking furnace, and a steam cracking system, as well as the application of the cracking furnace and the cracking system in steam cracking. Background Technology

[0002] To fully utilize crude oil resources and increase the yield of low-carbon olefins, cracking furnaces are typically used to crack various hydrocarbon feedstocks into olefins via steam cracking. Commonly used cracking furnaces include convection sections and radiation sections. Crude oil is generally divided into four components: saturated fractions, aromatic fractions, resins, and asphaltenes. Among these, saturated fractions and asphaltenes represent the most stable and least stable components of crude oil, respectively.

[0003] Crude oil contains high-molecular-weight non-volatile components with boiling points exceeding 590℃. During preheating in the convection section of a conventional cracking furnace, a small portion of these non-volatile components remains unvaporized. These unvaporized droplets linger on the inner surface of the furnace tubes in the convection section. Due to their high viscosity, they are difficult to flow and gradually accumulate, easily coking and depositing carbon at 350-600℃, even clogging the furnace tubes and affecting the yield of low-carbon olefins. This is a major reason why crude oil was not previously used as a cracking feedstock. Furthermore, coking often occurs in the convection section of the cracking furnace, a relatively low-temperature region. Once coking occurs in the convection section, it cannot be removed by online coking methods, often requiring furnace shutdown for manual decoking, significantly impacting the online time of the cracking furnace. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of insufficient gasification, easy coking in the convection section, and low yield of low-carbon olefins when using crude oil cracking to produce low-carbon olefins in the existing technology. The invention provides a steam cracking method, a cracking furnace, and a steam cracking system, as well as the application of the cracking furnace and the cracking system in steam cracking. This method can reduce coking in the furnace tubes of the convection section of the cracking furnace, extend the coking cycle of the radiant section, and obtain a higher product yield.

[0005] To achieve the above objectives, a first aspect of the present invention provides a steam cracking method, the method being carried out in a cracking furnace, the cracking furnace including a convection section and a radiation section, the method comprising:

[0006] The pyrolysis feedstock is mixed with steam in the convection section and heated to the transverse temperature before entering the radiation section for steam pyrolysis reaction to obtain low-carbon olefins.

[0007] The inner surface of the furnace tube in the convection section undergoes surface modification treatment to reduce coking inside the furnace tube.

[0008] The temperature range is 350-500℃.

[0009] Preferably, the modification treatment includes at least one of superhydrophobic and oleophobic coating modification, inert coating modification, and oxide film modification.

[0010] A second aspect of the present invention provides a pyrolysis furnace, the pyrolysis furnace comprising a convection section and a radiation section connected in series;

[0011] The inner surface of the furnace tube in the convection section is modified to reduce coking inside the furnace tube;

[0012] The convection section is used to contact the pyrolysis feedstock with steam and heat it to a cross temperature. The number of convection section tubes is sufficient to make the cross temperature range from 350 to 500°C.

[0013] A third aspect of the present invention provides a steam pyrolysis system comprising a pyrolysis furnace as described above.

[0014] The fourth aspect of the present invention provides the application of the pyrolysis furnace or steam pyrolysis system described above in steam pyrolysis.

[0015] The method described in this invention is used to gasify and steam crack the pyrolysis feedstock, and control the temperature across the range of 350-500℃. While maintaining the normal progress of the pyrolysis reaction in the radiant section, it can reduce coking in the pyrolysis furnace tubes, especially in the convection section, avoid the shutdown process required for coking removal in the convection section, and extend the coking cycle in the radiant section. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The first aspect of the present invention provides a steam cracking method, which is carried out in a cracking furnace including a convection section and a radiation section, the method comprising:

[0018] The pyrolysis feedstock is mixed with steam in the convection section and heated to the transverse temperature before entering the radiation section for steam pyrolysis reaction to obtain low-carbon olefins.

[0019] The inner surface of the furnace tube in the convection section undergoes surface modification treatment to reduce coking inside the furnace tube.

[0020] The temperature range is 350-500℃.

[0021] In this invention, the spanning temperature can be, for example, 350, 360, 380, 400, 420, 430, 435, 440, 445, 450, 455, 460, 465, 470, 475, 480, 490, 500°C, or any range between any two values; preferably, the spanning temperature is 430-480°C. The aforementioned spanning temperature can be achieved by reducing the number of mixing heating section tubes in the convection section and adjusting the set temperature.

[0022] In this invention, the cracking feedstock is the cracking feedstock in the conventional sense in the art. Specifically, the cracking feedstock may include light naphtha, naphtha, diesel, hydrotreated tail oil, light crude oil, crude oil with a final boiling point higher than 600°C and lower than 700°C, and dehydrated and desalted crude oil.

[0023] Preferably, the pyrolysis feedstock is selected from at least one of diesel oil, hydrotreated tail oil, light crude oil, dehydrated and desalted crude oil, and crude oil with a final boiling point higher than 600°C and lower than 700°C.

[0024] Preferably, the API degree of the pyrolysis feedstock is greater than 18, more preferably greater than 22, for example, it can be 24, 26, 28, 30, 32, 34, 36, 38, 40 or more, or any range between any two values.

[0025] API density is a measure developed by the American Petroleum Institute (API) to express the density of petroleum and petroleum products. API density is obtained by measuring the density of the raw material and then converting it.

[0026] In this invention, low-carbon olefins refer to olefins with fewer carbon atoms, such as olefins with four or fewer carbon atoms.

[0027] In this invention, the surface modification treatment preferably includes at least one of superhydrophobic and oleophobic coating modification, inert coating modification, and oxide film modification.

[0028] The superhydrophobic and oleophobic modification method can be the method provided in CN103091426A, the entire contents of which are incorporated herein by reference. For example, a superhydrophobic and oleophobic coating can be used to treat the inner surface of the convection section furnace tube. The treatment method can be a conventional method in the art, such as sequentially coating or impregnating, drying, and calcining (the calcination temperature can be 300-600℃, and the time can be 8-24h).

[0029] Preferably, the superhydrophobic and oleophobic coating comprises nano-metal oxides and polymers, and optionally also contains organic solvents.

[0030] Preferably, the nano-metal oxide is nano-titanium dioxide and / or nano-silicon dioxide.

[0031] Preferably, the polymer is selected from at least one of polysiloxanes and their derivatives, epoxy resins, and polyurethanes. Preferably, the polysiloxanes and their derivatives are selected from at least one of polydimethylsiloxane, hydrogen-containing polysiloxanes, and fluorinated polysiloxanes.

[0032] Both the nano-metal oxides and polymers mentioned above are commercially available.

[0033] The mass ratio of the nano-metal oxide to the polymer is preferably 0.8-7:1, more preferably 1-4:1.

[0034] The organic solvent can be a conventional solvent such as ethanol and acetone. When the coating contains an organic solvent, the content of the organic solvent in the superhydrophobic and oleophobic coating is 50-85 wt%.

[0035] In this invention, the method for modifying the inert coating can be the method provided in CN102899067A, the contents of which are incorporated herein by reference in their entirety.

[0036] In this invention, the method for modifying the oxide film can be the method provided in CN102807887A, the contents of which are incorporated herein by reference in their entirety.

[0037] Preferably, the method further includes: preheating the pyrolysis feedstock in a convection section before mixing the steam with the pyrolysis feedstock to obtain a preheated feedstock.

[0038] Preferably, the temperature of the preheated raw material is 120-300℃, more preferably 150-250℃.

[0039] To fully utilize the heat from the high-temperature flue gas in the radiant section, the convection section of the pyrolysis furnace is typically equipped with multiple sections for heat recovery. Generally, the convection section may include a feedstock preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section. The feedstock preheating section is typically used to preheat the pyrolysis feedstock. The boiler feedwater preheating section is typically used to preheat the boiler feedwater supplied to the steam drum. The dilution steam superheating section is typically used to preheat dilution steam (such as steam). The ultra-high pressure steam superheating section is typically used to heat the high-pressure steam from the steam drum to obtain ultra-high pressure steam. The mixing heating section is typically used to heat the pyrolysis feedstock to a temperature range. In this preferred embodiment, in the convection section, along the flow direction of the high-temperature flue gas, the mixing heating section, the ultra-high pressure steam superheating section, the dilution steam superheating section, the boiler feedwater preheating section, and the feedstock preheating section are preferably arranged sequentially.

[0040] The convection section preferably comprises a first convection section tube group (including a feedstock preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section) and a second convection section tube group (including a mixing heating section). The crude oil undergoes thorough gasification in the first convection section tube group, effectively improving the steam cracking efficiency.

[0041] Preferably, the temperature of the water vapor is 480-560℃, more preferably 500-540℃.

[0042] Preferably, the weight ratio of crude oil to water vapor is 1-4:1, more preferably 1.5-2.5:1.

[0043] In the radiant section, the material reaching the specified temperature is pyrolyzed. Preferably, the pyrolysis reaction conditions include: the outlet temperature of the radiant section is 780-850°C, more preferably 790-840°C. The outlet pressure of the radiant section is preferably 0.05-0.15 MPaG.

[0044] In this invention, the radiant section includes multi-pass furnace tubes, preferably 2-6 passes, and more preferably two passes.

[0045] The two-stage furnace tube can be, for example, a first stage consisting of two parallel vertical inlet tubes and a second stage consisting of one vertical outlet tube, forming a 2-1 type radiant furnace tube; or a first stage consisting of four parallel vertical inlet tubes and a second stage consisting of one vertical outlet tube, forming a 4-1 type radiant furnace tube.

[0046] Preferably, the ratio of the inner diameter of the outlet pipe to the inner diameter of the inlet pipe of the multi-pass furnace tube is greater than 1 and less than or equal to 2.5.

[0047] In a preferred embodiment of the present invention, the inner diameter of the inlet pipe of the multi-pass furnace tube ranges from 25 mm to 70 mm, more preferably from 40 mm to 65 mm.

[0048] In a preferred embodiment of the present invention, the inner diameter of the outlet pipe of the multi-pass furnace tube ranges from 45 mm to 120 mm, more preferably from 60 mm to 95 mm.

[0049] The radiant section of the furnace tube may also employ enhanced heat transfer elements. These elements can be various known or unknown components, such as spiral blade inserts, twisted ribbon inserts, cross-serrated inserts, coil core inserts, spiral wire porous bodies, spherical substrate inserts, etc., to facilitate heat transfer. Different enhanced heat transfer elements can also be added to different parts of the furnace tube.

[0050] In this invention, the pyrolysis furnace can be used together with other conventional equipment to achieve steam pyrolysis, such as being equipped with a quenching device, a steam drum, a blower, and a pyrolysis gas main.

[0051] Preferably, the method further includes: separating the pyrolysis products to obtain low-carbon olefins.

[0052] The material obtained after pyrolysis in the radiation section can first enter a quenching device for cooling and separation into pyrolysis gas and steam. The quenching device can be a conventional quenching device in the art, such as a quenching heat exchanger.

[0053] Unless otherwise specified, the methods and equipment involved in this invention are conventional methods and equipment in the art.

[0054] A second aspect of the present invention provides a pyrolysis furnace, the pyrolysis furnace comprising a convection section and a radiation section connected in series;

[0055] The inner surface of the furnace tube in the convection section is modified to reduce coking inside the furnace tube;

[0056] The convection section is used to contact the pyrolysis feedstock with steam and heat it to a cross temperature. The number of convection section tubes is sufficient to make the cross temperature range from 350 to 500°C.

[0057] The specific structure and modification methods of each piece of equipment involved have already been described in the first aspect and will not be repeated here. Unless otherwise specified, the equipment used has a conventional structure in this field.

[0058] A third aspect of the present invention provides a steam pyrolysis system comprising a pyrolysis furnace as described above.

[0059] It should be understood that the system may also include other supporting facilities, such as a quenching device, for cooling the pyrolysis material from the radiant section and separating it into low-carbon olefins. Preferably, the material inlet of the quenching device is connected to the material outlet of the radiant section.

[0060] The fourth aspect of the present invention provides the application of the pyrolysis furnace or steam pyrolysis system described above in steam pyrolysis.

[0061] The present invention will be described in detail below through embodiments.

[0062] In the following examples, the pyrolysis feedstock used was dehydrated and desalted crude oil with a density of 862.4 kg / m³ at 20°C. 3 The API level is approximately 33.

[0063] The cracking furnace used in the following examples is a modified version of the CBL-III cracking furnace purchased from Sinopec, and is used as the cracking furnace in Example 1.

[0064] Example 1

[0065] This embodiment illustrates a method for steam cracking crude oil.

[0066] The cracking reaction takes place in a steam cracking system, which includes a cracking furnace and a quench boiler connected in series. The cracking furnace includes a convection section (comprising a first and second convection section) and a radiation section connected in series; the material outlet of the radiation section is connected to the material inlet of the quench boiler. The convection section of the cracking furnace (comprising a first and a second convection tube group) includes a feedstock preheating section, a boiler feedwater preheating section, a dilution steam superheating section, an ultra-high pressure steam superheating section, and a mixing heating section. The feedstock preheating section is used to preheat crude oil; the boiler feedwater preheating section is used to preheat boiler feedwater supplied to the steam drum; the dilution steam superheating section is used to preheat dilution steam (such as water vapor); the ultra-high pressure steam superheating section is used to heat high-pressure steam from the steam drum to obtain ultra-high pressure steam; and the mixing heating section is used to heat crude oil to a temperature range.

[0067] The modification methods for the pyrolysis furnace include: (1) reducing the number of two sets of mixed heating section tubes in the pyrolysis furnace; (2) using nano-TiO2 composite coating (containing nano-titanium dioxide, polydimethylsiloxane and ethanol, prepared by mixing, wherein the mass ratio of nano-titanium dioxide to polydimethylsiloxane is 2 and the ethanol concentration is 80wt%), immersing the tubes of the convection section of the pyrolysis furnace in the coating solution for 2 hours, air drying for 2 hours, and then calcining at 420℃ for 10 hours to perform superhydrophobic and oleophobic coating treatment, forming a low surface tension ultra-micro nanostructure, with the wall surface distributed with ultra-micro structures of about 100 nanometers and small protrusions of about 10 micrometers.

[0068] The steam cracking method involves: crude oil at 60°C is vaporized and preheated in the convection section, then heated to the cross temperature (XOT) of 450°C, before entering the radiant section furnace tubes for cracking. The crude oil feed rate is 47,000 kg / h, and the dilution steam rate is 37,600 kg / h. The radiant section outlet temperature (COT) of the cracking furnace is 790°C, and the radiant section outlet pressure (COP) is 0.1 MPaG. The radiant section furnace tubes are two-pass tubes with an inlet diameter of 51 mm, an outlet diameter of 73 mm, and a tube length of 13.3 m.

[0069] Following the method described in Example 1, the pyrolysis products yielded 23.35% ethylene, 13.26% propylene, 5.41% butadiene, and 42.02% triene yields (the sum of the yields of ethylene, propylene, and butadiene). The pyrolysis furnace operated for 69 days, with online coking occurring 5 times per year, each coking lasting 2 days.

[0070] Example 2

[0071] This embodiment illustrates a method for steam cracking crude oil.

[0072] The operation is carried out according to the method described in Example 1, except that the method for modifying the convection section is the inert coating modification method described in CN102899067A. Specifically, the method of Example 1 is used to form an inert coating on the surface of the pyrolysis furnace tube.

[0073] Following the method of Example 2, the ethylene yield in the cracking products was 23.28%, the propylene yield was 13.57%, the butadiene yield was 5.28%, and the triene yield (the sum of the yields of ethylene, propylene, and butadiene) was 42.13%. The cracking furnace had an operating cycle of 69 days, with online coking occurring 5 times a year, each coking lasting 2 days.

[0074] Example 3

[0075] This embodiment illustrates a method for steam cracking crude oil.

[0076] The operation is carried out according to the method described in Example 1, except that the method for modifying the convection section is the oxide film modification method described in CN102807887A. Specifically, the method of Example 1 is used to form a metal oxide film protective layer on the surface of the pyrolysis furnace tube.

[0077] Following the method described in Example 3, the ethylene yield was 23.41%, the propylene yield was 13.20%, the butadiene yield was 5.16%, and the triene yield (the sum of the yields of ethylene, propylene, and butadiene) was 41.77%. The cracking furnace had an operating cycle of 71 days and was coked online 5 times a year, with each coking session lasting 2 days.

[0078] Comparative Example 1

[0079] This comparative example is used to illustrate the reference steam cracking method.

[0080] The pyrolysis was carried out in a steam pyrolysis system consisting of a CBL-III type pyrolysis furnace and a quench boiler connected in series with it. That is, unlike Example 1, the pyrolysis furnace of this system has two more sets of mixing heating section tubes in the convection section, and the convection section has not been modified with a superhydrophobic and oleophobic coating.

[0081] The procedure was performed according to the method in Example 1, except that the temperature range was 520°C.

[0082] The pyrolysis products yielded 23.01% ethylene, 13.02% propylene, and 5.05% butadiene, with a total yield of 41.08% (the sum of the yields of ethylene, propylene, and butadiene). The pyrolysis furnace had a 65-day operating cycle, with one coking cleaning of the convection section per year (7 days, plus one shutdown and one start-up). There were 5 online coking cycles, each lasting 2 days.

[0083] Compared with Comparative Example 1, Examples 1-3 increased or decreased the heat exchange tube array in the convection section and the mixing heating section. By reducing the heat exchange between the raw material and steam mixture and the flue gas in the mixing heating section, the cross temperature of the material was reduced compared with Comparative Example 1 (520°C). This effectively reduced the cracking reaction in the convection section and reduced coking.

[0084] Compared with Comparative Example 1, Examples 1-3 adopted superhydrophobic and oleophobic coatings, inert coatings, and oxide films, respectively, which reduced coking in the furnace tubes and improved the yield of pyrolysis products. The yield of trienes increased by 0.94%, 1.05%, and 0.69%, respectively. Moreover, the online time of the pyrolysis furnace was extended, the yield of the main pyrolysis products increased slightly, and a large amount of products were produced.

[0085] In addition, compared with Comparative Example 1, Examples 1-3 save on start-up, shutdown, and maintenance costs.

[0086] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A steam cracking process characterized in that, The method is implemented in a pyrolysis furnace, which includes a convection section and a radiation section, and the method includes: The pyrolysis feedstock is mixed with steam in the convection section and heated to the transverse temperature before entering the radiation section for steam pyrolysis reaction to obtain low-carbon olefins. The inner surface of the furnace tube in the convection section undergoes surface modification treatment to reduce coking inside the furnace tube. The surface modification treatment is a superhydrophobic and oleophobic coating modification. The superhydrophobic and oleophobic coating modification includes treating the inner surface of the convection section furnace tube with a superhydrophobic and oleophobic coating. The superhydrophobic and oleophobic coating contains nano-metal oxides and polymers. The nano-metal oxides are nano-titanium dioxide and / or nano-silica, and the polymers are selected from at least one of polysiloxanes and their derivatives, epoxy resins, and polyurethanes. The superhydrophobic and oleophobic coating modification results in the distribution of fine protrusions with a height of 10-20 micrometers on the inner surface of the furnace tube in the convection section, and these fine protrusions are composed of ultrafine structures with a particle size of 50-100 nanometers. The temperature range is 430-480℃. The radiant section includes a multi-pass furnace tube, the inner diameter of the inlet tube of the multi-pass furnace tube is 25-70mm, the inner diameter of the outlet tube of the multi-pass furnace tube is 45-120mm, and 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 greater than 1 and less than or equal to 2.

5.

2. The method of claim 1, wherein, The API degree of the pyrolysis feedstock is 18 or higher.

3. The method of claim 2, wherein, The API degree of the pyrolysis feedstock is 22 or higher.

4. The method of claim 3, wherein, The pyrolysis feedstock is selected from naphtha, diesel, hydrotreated tail oil, light crude oil, crude oil with a final boiling point above 600°C and below 700°C, and dehydrated and desalted crude oil.

5. The method of claim 4, wherein, The pyrolysis feedstock is selected from at least one of diesel oil, hydrotreated tail oil, light crude oil, dehydrated and desalted crude oil, and crude oil with a final boiling point higher than 600°C and lower than 700°C.

6. The method of claim 1, wherein, The temperature of the water vapor is 480-560℃; and / or The weight ratio of the pyrolysis feedstock to steam is 1-4:

1.

7. The method of claim 6, wherein, The temperature of the water vapor is 500-540℃; and / or The weight ratio of the pyrolysis feedstock to steam is 1.5-2.5:

1.

8. The method of any one of claims 1-7, wherein, The method further includes: preheating the pyrolysis feedstock in a convection section before mixing the steam with the pyrolysis feedstock to obtain a preheated feedstock.

9. The method according to claim 8, wherein, The temperature of the preheated raw material is 120-300℃.

10. The method according to claim 9, wherein, The temperature of the preheated raw material is 150-250℃.

11. The method according to claim 8, wherein, The conditions for the pyrolysis reaction include: the outlet temperature of the radiation section is 780-850℃.

12. The method according to claim 11, wherein, The conditions for the pyrolysis reaction include: the outlet temperature of the radiation section is 790-840℃.

13. A pyrolysis furnace, characterized in that, The pyrolysis furnace includes a convection section and a radiation section connected in series; The inner surface of the furnace tube in the convection section is modified to reduce coking inside the furnace tube. The surface modification treatment is a superhydrophobic and oleophobic coating modification. The superhydrophobic and oleophobic coating modification includes treating the inner surface of the convection section furnace tube with a superhydrophobic and oleophobic coating. The superhydrophobic and oleophobic coating contains nano-metal oxides and polymers. The nano-metal oxides are nano-titanium dioxide and / or nano-silica, and the polymers are selected from at least one of polysiloxanes and their derivatives, epoxy resins, and polyurethanes. The superhydrophobic and oleophobic coating modification results in the distribution of fine protrusions with a height of 10-20 micrometers on the inner surface of the furnace tube in the convection section, and these fine protrusions are composed of ultrafine structures with a particle size of 50-100 nanometers. The convection section is used to contact the pyrolysis feedstock with steam and heat it to a cross temperature. The number of convection section furnace tubes enables the cross temperature to be between 430-480°C. The radiant section includes a multi-pass furnace tube, the inner diameter of the inlet tube of the multi-pass furnace tube is 25-70mm, the inner diameter of the outlet tube of the multi-pass furnace tube is 45-120mm, and 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 greater than 1 and less than or equal to 2.

5.

14. A steam cracking system comprising the cracking furnace of claim 13.

15. The application of the pyrolysis furnace of claim 13 or the steam pyrolysis system of claim 14 in steam pyrolysis.