WO2025101290A1

WO2025101290A1 - Methods and systems for preparing gas-phase feedstock

Info

Publication number: WO2025101290A1
Application number: PCT/US2024/049694
Authority: WO
Inventors: Daniel BENEKE; Henk Hagen
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2023-11-08
Filing date: 2024-10-03
Publication date: 2025-05-15
Anticipated expiration: 2026-05-08

Abstract

Embodiments of the present disclosure are directed towards a method and system for preparing a gas-phase feedstock. The method and system for preparing a gas-phase feedstock for a reactor section of a cracking furnace having a convection section coupled to the reactor section includes preheating a hydrocarbon blend in a feed preheating exchanger (FPH) located in the convection section of the cracking furnace to form a preheated hydrocarbon blend, where the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and a circular feedstock oil. The method and system also includes mixing the preheated hydrocarbon blend with dilution steam to form a hydrocarbon-water gas-liquid feed mixture, separating the hydrocarbon-water gas-liquid feed mixture into a liquid phase and the gas-phase feedstock, and supplying the gas-phase feedstock to a high temperature coil exchanger (HTC) of the cracking furnace.

Description

Methods and Systems for Preparing Gas-Phase Feedstock

Field of Disclosure

[0001 ] Embodiments of the present disclosure are directed to preparing gas-phase feedstock for a cracking furnace system.

Background

[0002] The production of the raw materials that are used for the production of plastic products, e.g., ethylene and propylene, from fossil-based feedstocks such as ethane, propane and naphtha in the steam cracking industry can cause a negative effect on the environment. For instance, the steam cracking industry can cause fossil-based emissions to be released into the air. As such, there is a drive for reducing fossil-based emissions and waste. One way of doing this is to use feedstocks that are classified as circular. Such circular feedstocks can be obtained via the anaerobic thermal treatment of waste plastics, which is also known as pyrolysis. However, some circular feedstocks can have much higher boiling points than typical fossil-based feedstocks which could lead to poor vaporization and cause fouling in the cracking furnace’s preheating section due to its design for typical fossil-based feedstocks. To prevent fouling in the preheating section of the cracking furnace, the boiling range of the circular feedstock should be reduced or, alternatively, blended with lower boiling material to improve the evaporative behavior.

[0003] However, reducing the final boiling point of the circular feedstock would imply separating the lighter fraction from the heavier fraction by means of distillation. Separating the lighter fraction with distillation is an energy intense operation, which could increase the overall greenhouse gas emissions of the plastic recycling process, thereby negatively affecting the environment. Furthermore, distillation of the circular feedstock into a lighter and a heavier fraction, where the lighter fraction is suitable as steam cracker feedstock, leaves the heavier fraction to be used in, e.g., fuel applications. The use of the heavier fraction in a non-cracker application means that the overall plastics to plastics recycling yield, as defined by mass flow of circular olefins / mass flow of waste plastic used to produce a circular feedstock, is lowered. As such, there remains a need for an environmentally friendly means of using circular feedstock to produce olefins and plastics.

Summary

[0004] The present disclosure provides for a method and system for preparing a gasphase feedstock to be used in a reactor section of a cracking furnace that helps to overcome the above identified disadvantages of existing cracking furnace systems. For example, the method and system of the present disclosure can help provide for a reduction in the amount of energy needed to effectively use circular feedstock oil in the gas-phase feedstock. In addition, the method and system of the present disclosure help to process the circular feedstock oil in the gas-phase feedstock in such a way that reduces the likelihood of fouling in the reactor section of the cracking furnace. As discussed herein, such a method and system utilize a separator, as discussed herein, whose integration into the cracking furnace system helps to effectively process a hydrocarbon blend that includes the circular feedstock oil to produce the gas-phase feedstock, thereby maximizing the overall plastics to plastics recycling yield.

[0005] For the present disclosure, there is provided a method and system for preparing the gas-phase feedstock for a reactor section of a cracking furnace, where the cracking furnace includes a convection section coupled to the reactor section, as discussed herein. To prepare the gas-phase feedstock for the reactor section, the method of the present disclosure includes preheating a hydrocarbon blend in a feed preheating exchanger (FPH), located in the convection section of the cracking furnace, to form a preheated hydrocarbon blend, where the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and the, potentially heavier, circular feedstock oil; mixing the preheated hydrocarbon blend with dilution steam to form a hydrocarbon-water gas-liquid feed mixture; separating the hydrocarbon-water gas-liquid feed mixture into a liquid phase and the gas-phase feedstock; and supplying the gas-phase feedstock to a high temperature coil exchanger (HTC) of the cracking furnace.

[0006] For the present disclosure, the hydrocarbon blend can include 0 to 100 weight percent (wt.%) of the fossil-based hydrocarbon feedstock and 100 to 0 wt.% of the circular feedstock oil, where the wt. % is based on the total weight of the hydrocarbon blend. For the present disclosure, the fossil-based hydrocarbon feedstock can be selected from the group consisting of naphtha, ethane, propane, butane, gasoline, jet fuel, light gas oils and combinations thereof. For the present disclosure, the circular feedstock oil can be selected from the group consisting of oil from pyrolyzed waste plastic, oil from pyrolyzed waste tires, waste lubricant derived fuels, hydrotreated vegetable oil (HVO), sustainable aviation fuel (SAF) and combinations thereof. In some embodiments, the circular feedstock oil is formed from ethylene polymers and propylene polymers. In some embodiments, the circular feedstock oil can be formed with waste plastics. In some embodiments the circular feedstock oil has undergone a treatment to remove elements such a nitrogen, oxygen, chloride, such as hydroprocessing. For the present disclosure, the circular feedstock oil can have a boiling point range of 50 degrees Celsius (°C) to 645 °C. For the present disclosure, the circular feedstock oil can include a heavy feedstock of C4 to C60 hydrocarbons.

[0007] In some embodiments, the convection section can be preheated to a temperature ranging from 550 °C to 650 °C before entering the radiant (or reactive) section of the furnace. [0008] For the present disclosure, mixing the preheated hydrocarbon blend with dilution steam to form the hydrocarbon-water gas-liquid feed mixture can comprise mixing the preheated hydrocarbon blend in a convection section of the cracking furnace. For the present disclosure, the cracking furnace can include a separator coupled to the convection section. For the present disclosure, the separator can be used to separate the hydrocarbon-water gas-liquid feed mixture into the liquid phase and the gas-phase feedstock. In some embodiments, the separator can be a knockout drum. For example, the separator can be selected from a group comprising a knockout drum, cyclone separator, gravity separator, flotation separator, or combinations thereof.

[0009] The present disclosure further includes a cracking furnace system. The cracking furnace system includes the cracking furnace having a reactor section and a convection section attached to the reactor section. For the present disclosure, the reaction section provides heat to the convention section, as discussed herein. For the present disclosure, the convection section can include the feed preheating exchanger (FPH) to preheat a hydrocarbon blend to form a preheated hydrocarbon blend with the heat from the reaction section, where the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and the circular feedstock oil; a dilution steam super-heater (DSSH) to produce super-heated steam, where the super-heated steam is mixed with the preheated hydrocarbon blend to form a hydrocarbon-water gas-liquid feed mixture; and a high temperature coil exchanger (HTC). For the embodiments, the cracking furnace system can include a separator, as discussed herein, to receive the hydrocarbon-water gas-liquid feed mixture, where the separator produces a liquid phase and a gas-phase feedstock from the hydrocarbon-water gas-liquid feed mixture, and where the gas-phase feedstock is supplied to the HTC of the convection section of the cracking furnace. In some embodiments, the separator can be external to the cracking furnace system.

Brief Description of the Drawings

[0010] FIG. 1 . is a schematic diagram of a typical cracking furnace in a steam cracking plant.

[0011 ] FIG. 2 is a schematic view of a cracking furnace system that includes a separator in accordance with the described embodiment. [0012] FIG. 3 is a graph showing production characteristics when using a cracking furnace system of the present disclosure.

Detailed Description

[0013] The present disclosure provides for a process for preparing gas-phase feedstock for a cracking furnace. More specifically, the present disclosure relates to preparing a feed containing fossil-based hydrocarbon feedstock and circular feedstock oil for cracking by using a separator and heat from the convection section of the cracking furnace to separate a hydrocarbon-water gas-liquid feed mixture into a liquid phase and a gas-phase feedstock. In this way, the present disclosure helps to better ensure that a feed to the reaction section containing a higher boiling point is fully vaporized for cracking, as unvaporized hydrocarbons present in the feed can present significant fouling risks. For example, if liquid is present, droplets may deposit on inner tube walls and undergo thermal degradation which can lead to coke formation. The method and systems described in the present disclosure allow for higher boiling point circular feedstock oil to be used without significant risk of fouling, while helping to lower the overall greenhouse gas emissions during the cracking process.

[0014] As used herein, high-pressure steam refers to steam having a pressure of 90 bar to 125 bar and a temperature of 320 °C to 550 °C.

[0015] As used herein, recited values can be proceeded by the word approximately. For example, high-pressure steam refers to steam having a pressure of approximately 90 bar to approximately 125 bar and a temperature of approximately 320 °C to approximately 550 °C.

[0016] As used herein, saturated steam refers to water that has been vaporized, where both liquid and gas phases are in equilibrium.

[0017] As used herein reactor section refers to the portion of a cracking furnace where steam cracking takes place. As used herein, steam cracking refers to a process in which heat is used to break hydrocarbon molecules down into lighter molecules.

[0018] In preparing the gas-phase feedstock for a reactor section, the method of the present disclosure includes preheating a hydrocarbon blend in a feed preheating exchanger (FPH), located in the convection section of the cracking furnace, to form a preheated hydrocarbon blend, where the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and the circular feedstock oil; mixing the preheated hydrocarbon blend with dilution steam to form a hydrocarbon-water gas-liquid feed mixture; separating the hydrocarbon-water gas-liquid feed mixture into a liquid phase and the gas-phase feedstock; and supplying the gasphase feedstock to a high temperature coil exchanger (HTC) of the cracking furnace. [0019] In some embodiments, the hydrocarbon blend can include 0 to 100 wt.% of the fossil-based hydrocarbon feedstock and 100 to 0 wt.% of the circular feedstock oil, where the wt. % is based on the total weight of the hydrocarbon blend. In a preferred embodiment, the hydrocarbon blend can include 25 to 99 wt.% of the fossil-based hydrocarbon feedstock and 75 to 1 wt.% of the circular feedstock oil, where the wt. % is based on the total weight of the hydrocarbon blend. In a more preferred embodiment, the hydrocarbon blend can include 50 to 95 wt.% of the fossil-based hydrocarbon feedstock and 50 to 5 wt.% of the circular feedstock oil, where the wt. % is based on the total weight of the hydrocarbon blend. In a most preferred embodiment, the hydrocarbon blend can include 75 to 90 wt.% of the fossil-based hydrocarbon feedstock and 25 to 10 wt.% of the circular feedstock oil, where the wt. % is based on the total weight of the hydrocarbon blend. In some embodiments, the fossil-based hydrocarbon feedstock can be selected from the group consisting of naphtha, ethane, propane, butane, gasoline, jet fuel, light gas oils and combinations thereof. In various embodiments, the circular feedstock oil can be selected from the group consisting of oil from pyrolyzed waste plastic, oil from pyrolyzed waste tires, waste lubricant derived fuels, hydrotreated vegetable oil (HVO), sustainable aviation fuel (SAF) and combinations thereof.

[0020] For the embodiments, the hydrocarbon blend, as used herein, can be prepared by either feeding the circular feedstock oil and the fossil-based hydrocarbon feedstock in the desired proportions to a mix tank (e.g., a mix tank having an active mixing device such as an impeller) and/or by feeding the circular feedstock oil and the fossil-based hydrocarbon feedstock from separate tanks or storage structures into the furnace feed system in the desired proportions.

[0021 ] For the embodiments, the circular feedstock oil can be formed from waste plastics, where examples include ethylene polymers and propylene polymers. In some embodiments the circular feedstock oil can have undergone a treatment to remove elements such a nitrogen, oxygen, chloride, such as hydroprocessing, as is known in the art. In various embodiments, the oil from pyrolyzed waste plastic that can be present in the circular feed stock oil can have the characteristic as shown in Table 1 . The data from Table 1 was obtained from A. Gala, et al. Characterization and Distillation of Pyrolysis Liquids Coming from Polyolefins Segregated of MSW for Their Use as Automotive Diesel Fuel. Energy & Fuels 2020 Vol. 34 Issue 5 Pages 5969-5982, which is incorporated here by reference.

Table 1

Based at least on this, the circular feedstock oil can have a boiling point range of 50 degrees Celsius (°C) to 645 °C. In some embodiments, the circular feedstock oil can include a heavy feedstock of C4 to C60 hydrocarbons.

[0022] As described herein, a separator may be coupled to the convection section of the cracking furnace. In some embodiments, the convection section can be preheated to a temperature ranging from approximately 550 °C to 650 °C. In some embodiments, mixing the preheated hydrocarbon blend can comprise mixing the preheated hydrocarbon blend with dilution steam to form the hydrocarbon-water gas-liquid feed mixture in the convection section of the cracking furnace. In addition, as described herein, a separator can be used to separate the hydrocarbon-water gas-liquid feed mixture into the liquid phase and the gas-phase feedstock. In some embodiments, the separator can be selected from a group comprising a knockout drum, cyclone separator and combinations thereof.

[0023] In various embodiments, the cracking furnace system can include a cracking furnace having a reactor section and a convection section attached to the reactor section. In some embodiments, the reaction section can provide heat to the convention section. In various embodiments, the convection section can include a feed preheating exchanger (FPH) to preheat a hydrocarbon blend to form a preheated hydrocarbon blend with the heat from the reaction section. In some embodiments, the hydrocarbon blend can include a fossil-based hydrocarbon feedstock and the circular feedstock oil. In addition, in some embodiments, the convection section can include a dilution steam super-heater (DSSH) to produce super-heated steam. In some embodiments, the super-heated steam, produced by the DSSH, can be mixed with the preheated hydrocarbon blend to form a hydrocarbon-water gas-liquid feed mixture. In some embodiments, the convection section can further include a high temperature coil exchanger (HTC). For the embodiments, the cracking furnace system can include a separator, as discussed herein, to receive the hydrocarbon-water gas-liquid feed mixture. In various embodiments, the separator produces a liquid phase and a gas-phase feedstock from the hydrocarbon-water gas-liquid feed mixture. In some embodiments, the gas-phase feedstock can be supplied to the HTC of the convection section of the cracking furnace when produced. In some embodiments, the separator can be external to the cracking furnace system. [0024] FIG. 1 is a schematic diagram of a typical cracking furnace 99 in a steam cracking plant for ethylene production. The cracking furnace 99 in FIG. 1 is a generic example of a furnace. A cracking furnace similar to the generic furnace described herein can be found in R. Karimzadeh, et al. Flowsheeting of steam cracking furnaces. Chemical Engineering Research and Design Volume 87, Issue 1 , January 2009, Pages 36-46, which is incorporated here by reference. Alternative arrangements are possible. The cracking furnace 99 shown in FIG. 1 includes a convection section 12 containing a number of heat exchangers heated by flue gas from a reactor (or radiant) section 14. The convection section 12 can have a variety of layouts for each furnace design as would be known to one skilled in the art. In FIG. 1 the heat exchangers depicted in the convection section 12 can include a feed preheating exchanger (FPH) 16, an economizer bundle 18, a first high temperature coil (HTC-1) 20, a dilution steam super-heater (DSSH) 22, a first high-pressure superheater bundle (HPSSH1 ) 24, a second high- pressure superheater bundle (HPSSH2) 26, and a second high temperature coil (HTC-2) 28. The cracking furnace may also include a transfer line exchanger (TLE) 30. In the cracking furnace 99 arrangement depicted by FIG. 1 a liquid feed 31 is preheated and partially vaporized by the FPH 16 where flue gas temperatures are low. The preheated and partially vaporized feed 33 can be mixed with a small liquid petroleum gas (LPG) stream 37 in this cracking furnace 99 arrangement. Once the feed has been preheated, dilution steam 38 is preheated in the DSSH 22. These two streams can be mixed and fed into the downstream high temperature coil exchangers HTC-I 20 and HTC-II 28 to form a fully vaporized feed mixed with dilution steam (FVF) 40. The FVF 40 enters the reactor section 14 where long chain hydrocarbons in the vaporized feed are broken down into short chain olefins like ethylene and propylene, among others. Exiting the radiant section 14, a hot effluent 42 is rapidly cooled in the TLE 30 against preheated boiler feed water 44 (boiler feed water (BFW) 44 that has been preheated in the economizer bundle 18) to prevent secondary undesirable reactions. The preheated BFW 44 is vaporized in the TLE 30 to form saturated steam 48. The saturated steam 48 produced in the TLE 30 can, for example, have a temperature around 320 °C. The saturated steam 48 is further heated in in high-pressure superheater (HPSSH) bundles HPSSH1 24 and HPSSH2 26 in the convection section 12, to temperatures that can range from 450 °C to 550 °C, to form a high- pressure steam (HPS) 50. Boiler feed water 46 can also be injected between the HPSSH1 24 and HPSSH2 26 bundles to control the temperature of the final HPS 50 from HPSSH2 26. HPS 50 produced in the furnace can be utilized for driving downstream compressor turbines 57, can be let down to lower steam pressure levels for other consumers, or can be used for other purposes.

[0025] A particular problem with cracking circular feedstock oils (e.g., heavy feedstock) through this technique of mixing a stream of lighter hydrocarbons with a heavy feed, however, is that common design conditions of cracking furnaces can only ensure complete vaporization a feed containing a small percentage of circular feedstock oil. However, if a large amount of circular feedstock oil is used, liquids may still remain which can cause fouling in the cracking furnace’s preheating section.

[0026] FIG. 2 is a schematic view of a cracking furnace system 100 that includes a separator 60 in accordance with the described embodiment. The cracking furnace system 100 in FIG. 2 is a generic example of a furnace including a separator 60. The cracking furnace system 100 may be similar to a typical cracking furnace (e.g., cracking furnace 99 of FIG. 1 ). From a sustainability perspective, steam cracking of heavy liquid feeds such as hydro processed biobased oil e.g., hydrotreated vegetable oil), syngas liquid products, and hydrotreated waste plastic pyrolysis oil can help reduce the need for fossil-based feedstocks and help to decarbonize cracking furnaces. As heavier feedstocks can require more energy to vaporize, one approach for cracking heavy liquid feedstocks is to purpose-build a cracking furnace. The amount of heavier feedstock that can be fully vaporized can be limited in a cracking furnace that is not purpose-built for heavy liquid feedstocks, however, a purpose-build furnace can be expensive to implement. Another approach can be to use a cracking furnace coupled to a separator (separator 60) to allow cracking of a heavy hydrocarbon feedstock mixed with a stream of lighter hydrocarbons (e.g., naphtha). In this approach, the stream of lighter hydrocarbons helps to reduce the partial pressure of the heavy feedstock and the separator helps prevent liquid from entering the convection section and the reactor section of the cracking furnace.

[0027] More specifically this disclosure provides for a cracking furnace system 100 that can include a cracking furnace 10, having a reactor section 14, a convection section 12 attached to the reactor section, as discussed herein, and a separator 60 coupled to the convection section 12. The convection section 12 can contain a number of heat exchangers heated by flue gas from a reactor (or radiant) section 14. Similar to the convection section described in FIG. 1 , the heat exchangers in FIG. 2 can include a feed preheating exchanger (FPH) 16, an economizer bundle 18, a first high temperature coil (HTC-1 ) 20, a dilution steam super-heater (DSSH) 22, a first high- pressure superheater bundle (HPSSH1 ) 24, a second high-pressure superheater bundle (HPSSH2) 26, and a second high temperature coil (HTC-2) 28. The cracking furnace system 100 may also include a transfer line exchanger (TLE) 30.

[0028] In the cracking furnace system 100 arrangement depicted by FIG. 2 a hydrocarbon blend 32 is preheated and partially vaporized by the FPH 16 where flue gas temperatures are low. In some embodiments, the convection section 12 of the cracking furnace system 100 can be preheated to a temperature ranging from 550 °C to 650 °C. The hydrocarbon blend 32 can include fossil-based hydrocarbon feedstock and circular feedstock oil.

[0029] In various embodiments, dilution steam 38 is preheated in the DSSH 22 when the hydrocarbon blend 32 has been preheated. The preheated dilution stream 39 is mixed with the preheated hydrocarbon blend 34 to form a hydrocarbon-water gas-liquid feed mixture. In some embodiments, the preheated hydrocarbon blend 34 and the preheated dilution stream 39 are mixed in a separator 60. In one embodiment, the separator 60 is external to the cracking furnace system 100.

[0030] The hydrocarbon-water gas-liquid feed mixture is sent to the separator 60 in this cracking furnace system 100 arrangement. In some embodiments, the separator 60 separates the hydrocarbon-water gas-liquid feed mixture into a liquid phase 56 and the gas-phase feedstock 36. The gas-phase feedstock 36 can be fed into the downstream high temperature coil exchangers HTC-I 20 and HTC-II 28 to form a fully vaporized feed mixed with dilution steam (FVF) 40. The FVF 40 enters the reactor section 14 where long chain hydrocarbons in the vaporized feed are broken down into short chain olefins like ethylene and propylene, among others. Exiting the radiant section 14, a hot effluent 42 is rapidly cooled in the TLE 30 against preheated boiler feed water 44, that has been preheated in the economizer bundle 18, to prevent secondary undesirable reactions. [0031 ] FIG. 3 is a graph showing the benefits of using a cracking furnace system, such as for the cracking furnace system of the present disclosure to produce circular olefins. FIG. 3 shows along the x-axis the weight percent of pyrolyzed plastic oil (PPG) blended with naphtha, along the left y-axis the delta in yield of circular olefins (ethylene and propylene combined) between the present disclosure and the base case (e.g., not using the separator of the present disclosure), and along the right y-axis the energy intensity of upstream distillation needed for the base case scenario to allow the desired usage of weight percent of PPG blended with naphtha. Since the present disclosure does not require upstream distillation, the delta in energy intensity is equal to the value obtained for the base case but as a negative value. As illustrated in FIG. 3, as the wt.% of PPG present in the naphtha increases the energy requirement for the base case also increases, as seen by a continuous increase in the negative value of the delta energy intensity line. Furthermore, using the cracking furnace coupled to the separator according to the present disclosure and as described, for example, in FIG. 2, it is possible to increase the amount of circular olefins produced at an energy intensity that is lower than would be required for a separate distillation process. In other words, it is possible to increase the amount of circular olefins produced according to the present disclosure while reducing the energy intensity of the overall process, as an upstream distillation process is no longer necessary. Note in this example, all circular feedstock fed to the cracking furnace may be attributed to certain products on a mass balance basis (for instance, a feed of 1 ton of PPG allows for 1 ton of olefin products to be regarded as circular).

Claims

What is claimed is:

1 . A method for preparing a gas-phase feedstock for a reactor section of a cracking furnace having a convection section coupled to the reactor section, the method comprising: preheating a hydrocarbon blend in a feed preheating exchanger (FPH) located in the convection section of the cracking furnace to form a preheated hydrocarbon blend, wherein the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and a circular feedstock oil; mixing the preheated hydrocarbon blend with dilution steam to form a hydrocarbon-water gas-liquid feed mixture; separating the hydrocarbon-water gas-liquid feed mixture into a liquid phase and the gasphase feedstock; and supplying the gas-phase feedstock to a high temperature coil exchanger (HTC) of the cracking furnace.

2. The method of claim 1 , wherein the fossil-based hydrocarbon feedstock is selected from the group consisting of naphtha, ethane, propane, butane, gasoline, jet fuel, light gas oils and combinations thereof.

3. The method of any one of claims 1-2, wherein the circular feedstock oil is selected from the group consisting of oil from pyrolyzed waste plastic, oil from pyrolyzed waste tires, waste lubricant derived fuels, hydrotreated vegetable oil (HVO), sustainable aviation fuel (SAF) and combinations thereof.

4. The method of claim 3, wherein the circular feedstock oil has a boiling point range of 50 degrees Celsius (°C) to 645 °C.

5. The method of any one of claims 1-4, wherein the convection section is preheated to a temperature ranging from 550 °C to 650 °C.

6. The method of any one of claims 1-5, wherein the hydrocarbon blend includes 0 to 100 weight percent (wt.%) of the fossil-based hydrocarbon feedstock and 100 to 0 wt.% of the circular feedstock oil, wherein the wt. % is based on the total weight of the hydrocarbon blend.

7. The method of any one of claims 1-6, wherein the circular feedstock oil includes a heavy feedstock of C4 to C60 hydrocarbons.

8. The method of any one of claims 1-7, wherein the circular feedstock oil is formed from ethylene polymers and propylene polymers.

9. The method of any one of claims 1-8, wherein mixing the preheated hydrocarbon blend comprises mixing the preheated hydrocarbon blend in the convection section of the cracking furnace.

10. The method of claim 1 -9, further comprising using a separator to separate the hydrocarbon-water gas-liquid feed mixture into the liquid phase and the gas-phase feedstock.

11 . The method of claim 10, wherein the separator is a knockout drum.

12. The method of any one of claims 9-11 , wherein the separator is external to the cracking furnace.

13. A cracking furnace system, comprising; a cracking furnace, having: a reactor section; and a convection section attached to the reactor section, wherein the reaction section provides heat to the convention section and wherein the convection section includes: a feed preheating exchanger (FPH) to preheat a hydrocarbon blend to form a preheated hydrocarbon blend with the heat from the reaction section, wherein the hydrocarbon blend includes a fossil-based hydrocarbon feedstock and a circular feedstock oil; a dilution steam super-heater (DSSH) to produce super-heated steam, wherein the super-heated steam is mixed with the preheated hydrocarbon blend to form a hydrocarbon-water gas-liquid feed mixture; and a high temperature coil exchanger (HTC); and a separator to receive the hydrocarbon-water gas-liquid feed mixture, wherein the separator produces a liquid phase and a gas-phase feedstock from the hydrocarbon-water gas-liquid feed mixture, and wherein the gas-phase feedstock is supplied to the HTC of the convection section of the cracking furnace.

14. The cracking furnace system of claim 13, wherein the separator is a cyclone separator.

15. The cracking furnace system of any one of claims 13-14, wherein the separator is external to the cracking furnace.