Efficient cracking furnace system with reduced co2 emissions

Abstract

A cracking furnace system for converting a hydrocarbon feedstock to a cracked gas includes a convection section, a radiant section, and a cooling section. The convective section includes a plurality of convective groups configured to receive only a hydrocarbon feedstock and a diluent. The radiant section includes a combustion chamber including at least an oxygen or oxygen-enriched air flame jet and a number of radiant coils configured to heat the feedstock to a temperature that permits a pyrolytic reaction. The cooling section comprises at least two transfer line exchangers (TLE): a primary transfer line exchanger (PTLE) and a secondary transfer line exchanger (STLE). The system includes a mixing device for mixing a preheated hydrocarbon feedstock and a preheated diluent. The system is configured such that the hydrocarbon feedstock and diluent mixture is preheated in the secondary transfer line exchanger before entering the radiant section. The primary transfer line exchanger is configured to generate saturated steam. The system includes a steam drum connected to the primary transfer line exchanger.

Description

Background Art

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Patent Application No. 18 / 062,568, filed on December 6, 2022. The disclosure thereof is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a cracking furnace system for converting a hydrocarbon feedstock into cracked gas and a method for cracking a hydrocarbon feedstock in the cracking furnace system.

[0004] Related Art

[0005] As disclosed, for example, in document US 4479869, a conventional cracking furnace system generally includes a convection section in which a hydrocarbon feedstock is preheated and / or partially evaporated and mixed with dilution steam to provide a feedstock-dilution steam mixture. The system also includes a radiation section that includes at least one radiant coil in a combustion chamber, where the feedstock-dilution steam mixture 6 from the convection section is converted into product and by-product components by pyrolysis at a high temperature. The system also includes a cooling section that includes at least one quench exchanger, such as a transfer line exchanger, that is configured to rapidly quench the product or cracked gas leaving the radiation section to stop the pyrolysis side reactions and maintain a reaction equilibrium favorable to the product. Heat from the transfer line exchanger can be recovered in the form of high-pressure steam.

[0006] A disadvantage of known systems is the need to supply a large amount of fuel for the pyrolysis reaction.

[0007] Carbon capture and storage (CCS) is a commercial method to help petrochemical companies achieve carbon neutrality. CCS is an expensive method because it processes a large amount of flue gas and uses amines to extract CO2 from nitrogen. Oxygen fuel combustion is a solution for significantly reducing the amount of flue gas. Oxygen can be generated from an air separation unit or a water electrolyzer. In the case of oxygen fuel combustion, the flue gas contains 64 mol% water and 30 mol% CO2. The rest is a small amount of excess O2 and N2 inert gases. Since the heat of combustion is not used to heat a large amount of inert gases such as N2, the fuel gas consumption can be reduced by about 30%. Overall, the mass flow rate of the flue gas is reduced by more than 80%. This can significantly reduce the size of the CCS equipment and simplify the CO2 separation process. However, this poses new challenges to the design of ethylene cracking furnaces.

[0008] The convective ethylene furnace provides heat for the steam cracking reaction and heat for generating ultra-high pressure steam. The combustion of pure oxygen fuel without any additional inert gas or external recirculation of inert gas significantly reduces the available heat. There is not enough heat to provide the cracking heat in the radiant section and raise the hydrocarbon and dilution steam temperatures to the target crossover temperature.

[0009] This conventional method and system are generally considered satisfactory for their intended purposes. However, there is still a need in the art for a more efficient cracking furnace system that reduces the demand for energy supply and thus reduces CO2 emissions. The present disclosure provides a solution to this need. Summary of the Invention

[0010] A cracking furnace system for converting a hydrocarbon feedstock into cracked gas, the cracking furnace system including a convective section, a radiant section, a cooling section, and a steam drum. The convective section includes a plurality of convective groups configured to receive only the hydrocarbon feedstock and a diluent. The radiant section includes a combustion chamber that includes at least an oxygen or oxygen-enriched air burner and a number of radiant coils configured to heat the feedstock to a temperature that permits a pyrolysis reaction, wherein the cooling section includes at least two transfer line exchangers (TLEs): a primary transfer line exchanger (PTLE) and a secondary transfer line exchanger (STLE). The system further includes a mixing device configured and adapted to mix the preheated hydrocarbon feedstock and the preheated diluent. The system is configured such that the hydrocarbon feedstock and diluent mixture is preheated in the secondary transfer line exchanger before entering the radiant section. The primary transfer line exchanger is configured to generate saturated steam. The steam drum is connected to the primary transfer line exchanger.

[0011] In some embodiments, the diluent may be dilution steam. In certain embodiments, the surface area of the radiant coils in the radiant section may be constituted by serpentine coils. It is contemplated that the cooling section may include a tertiary transfer line exchanger. The radiant section includes an oxy-fuel burner. The cracking furnace system may include a flame temperature control device in the radiant section. The flame temperature control device may include a high-speed injector to introduce fuel and oxygen or oxygen-enriched air in the radiant section. In some embodiments, the convective section does not include utility units such as a boiling feed water economizer group and an ultra-high pressure steam superheater group configured to generate superheated steam.

[0012] A method for cracking a hydrocarbon feedstock in a cracking furnace system includes: preheating the feedstock in a convection section at a temperature between 50°C and 180°C; mixing the preheated hydrocarbon feedstock with a diluent to form a mixed feedstock-diluent; preheating the mixed feedstock-diluent in a secondary transfer line exchanger at a temperature between 250°C and 700°C; and cracking the preheated mixed feedstock-diluent by combustion with oxygen or oxygen-enriched air in a radiation section to produce cracked gas. The method includes cooling the cracked gas in a primary transfer line exchanger (PTLE), further cooling the cracked gas exiting the primary transfer line exchanger (PTLE) in a secondary transfer line exchanger (STLE), and generating saturated super-high pressure steam in the PTLE.

[0013] In certain embodiments, the saturated super-high pressure steam is generated from water from a steam drum. In some embodiments, the generated saturated super-high pressure steam is fed into the steam drum. The diluent can be dilution steam. The dilution steam can be generated outside the cracking furnace system. According to some embodiments, cracking the mixed feedstock-diluent includes controlling the combustion temperature in the radiation section by diluting the fuel and oxygen or oxygen-enriched air. The oxygen-enriched air can contain more than 21% oxygen. Cracking the mixed feedstock-diluent can include generating flue gas at a temperature between 950°C and 1300°C and sending the flue gas to the convection section. The method can include cracking the mixed feedstock-diluent, including generating flue gas at a temperature between 1000°C and 1150°C. Preheating the feedstock in the convection section can include preheating the feedstock in the convection section at a temperature between 150°C and 160°C. Preheating the mixed feedstock-diluent in the secondary transfer line exchanger can include preheating the mixed feedstock-diluent in the secondary transfer line exchanger at a temperature between 275°C and 500°C.

[0014] These and other features of the systems and methods of the present disclosure will become more apparent to those skilled in the art from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Accordingly, those skilled in the art of the present disclosure will readily understand how to make and use the devices and methods of the present disclosure without undue experimentation. Preferred embodiments herein will be described in detail below with reference to certain drawings, wherein:

[0016] Figure 1 A schematic diagram of a cracking furnace system according to a preferred embodiment of the present invention is shown. DETAILED DESCRIPTION

[0017] Reference will now be made to the accompanying drawings, in which like reference numerals identify similar structural features or aspects of the present disclosure. For purposes of explanation and illustration and not limitation, an exemplary embodiment of a cracking furnace system for converting a hydrocarbon feedstock in accordance with the present disclosure is shown in Figure 1 and is generally designated by reference numeral 100. The solution of the present invention is a cracking furnace system 100 for converting a hydrocarbon feedstock 1 into a cracked gas 9, the cracking furnace system including a convection section 2, a radiation section, and a cooling section, wherein the convection section 2 includes a plurality of convection groups configured to receive only the hydrocarbon feedstock 1 and a diluent 3,

[0018] - wherein the radiation section includes a combustion chamber including at least an oxygen or oxygen-enriched air burner and a plurality of radiant coils 8 configured to heat the feedstock to a temperature allowing a pyrolysis reaction,

[0019] - wherein the cooling section includes at least two transfer line exchangers (TLEs): a primary transfer line exchanger (PTLE) 10 and a secondary transfer line exchanger (STLE) 7,

[0020] - wherein the system further includes a mixing device, such as a mixing tee, etc., configured and adapted to mix the preheated hydrocarbon feedstock 4 and the preheated diluent 5,

[0021] - wherein the system is configured such that the hydrocarbon feedstock and diluent mixture 6 is preheated in the secondary transfer line exchanger 7 before entering the radiation section,

[0022] - wherein the primary transfer line exchanger 10 is configured to generate saturated steam 11, and the system further includes a steam drum 12 connected to the primary transfer line exchanger 10.

[0023] As is known to those skilled in the art, the optimum inlet temperature of the feedstock into the radiation section is determined by the thermal stability of the feedstock. Ideally, the feedstock enters the radiation section at a temperature just below the start point of the pyrolysis reaction. If the feedstock inlet temperature is too low, additional heat is required to heat the feedstock in the radiation section, thereby increasing the heat to be supplied in the radiation section and the corresponding fuel consumption. If the feedstock inlet temperature is too high, pyrolysis may have started in the convection section 2, which is undesirable because the reaction is associated with the formation of coke on the surface of the inner tubes and the coke cannot be easily removed in the convection section 2 during decoking. An advantage of the cracking furnace system of the present invention is that fouling by condensation of heavy (asphaltenic) tailings is almost impossible in the transfer line exchangers according to the present invention.

[0024] The transfer line exchanger (TLE) is a heat exchanger arranged to cool or quench the cracked gas 9. According to the present invention, using the waste heat of the cracked gas 9 in the transfer line exchanger to partially heat the feedstock instead of only heating the feedstock in the convection section 2 as in the prior art systems can allow a significant increase in the furnace efficiency. The furnace efficiency is the ratio between the heat absorbed by at least one radiant coil 8 for converting the hydrocarbon feedstock 1 into cracked gas 9 by pyrolysis (which is an endothermic reaction) and the heat released by the combustion process in the combustion zone, based on the lower heating value at 25 °C or 15.6 °C.

[0025] Preferably, the hydrocarbon feedstock 1 is naphtha or a lighter feed. A hydrocarbon and dilution steam mixture 6 can be used as a cooling medium to recover heat from the cracked gas 9. Heavy liquid feeds may have fouling problems on the transfer line exchanger. When cracking heavy liquid feeds, the ratio of dilution steam to hydrocarbon is high. Dilution steam can be used as a cooling medium to recover heat from the cracked gas 9.

[0026] In the radiant section, cracking heat must be provided to convert the hydrocarbon feed into olefins and other high-value products. If the flue gas temperature leaving the radiant section is the same as that of a conventional furnace, then due to an 80% reduction in the flue gas flow rate, the heat available in the convection section of an oxy-fuel ethylene cracking furnace is only 20% of the heat available in a conventional furnace. The available heat is not sufficient to raise the hydrocarbon feed and dilution steam to the target crossover temperature.

[0027] In the cooling section, the cracked effluent must be immediately cooled to stop side reactions and maintain the cracked gas yield. The cooling medium in a conventional furnace is saturated boiler feed water or cold boiler feed water.

[0028] The hydrocarbon feedstock 1 and the diluent 3 need to be further heated, and the cracked effluent needs to be cooled. The heat demand and heat supply are coupled together in the secondary transfer line exchanger 7. The tube side of the shell-and-tube exchanger is the cracked gas 9, and the shell side is the hydrocarbon feedstock and diluent mixture 6. The convection section 2 of the oxy-fuel ethylene cracking furnace only has a hydrocarbon and diluent preheating group. Then, the hydrocarbon feedstock 1 and the diluent 3 are mixed and directed to the shell side of the secondary transfer line exchanger 7 for superheating. After superheating in the secondary transfer line exchanger 7, the hydrocarbon feedstock and diluent mixture 6 is transported to the radiant section for cracking.

[0029] The primary transfer line exchanger 10 is a conventional boiler feed water quench exchanger. There is no economizer group for preheating the boiler feed water in the convection section 2, nor is there a superheated high-pressure steam group. The boiler feed water directly enters the steam drum 12. High-pressure steam is generated on the shell side of the primary quench exchanger and is output for superheating or utilization in the equipment. The waste heat in the convection section 2 is only used to preheat the feedstock and the diluent.

[0030] According to an embodiment, the cracking furnace system according to the present invention may include one or more of the following features:

[0031] - The diluent 3 is dilution steam.

[0032] - The surface area of the radiant coils 8 in the radiant section is formed by serpentine coils; these serpentine coils transfer heat from a heat source (such as a flame) to a radiator (such as hydrocarbons and dilution steam within the radiant coils 8);

[0033] - The cooling section includes a three-stage transfer line exchanger.

[0034] - The radiant section includes an oxy-fuel burner.

[0035] - The cracking furnace system has a flame temperature control device in the radiant section;

[0036] - The flame temperature control device includes a high-speed jet 17 to introduce fuel and oxygen or oxygen-enriched air 14 in the radiant section. The high-speed jet 17 entrains combustion chamber flue gas with internal flue gas recirculation and reduces the fuel and oxygen concentrations in the combustion zone; modern burner technology utilizes staged fuel and staged oxidizer to control the flame temperature. Both the fuel and oxygen have high supply pressures. Before mixing the fuel and oxygen, the fuel jet and oxygen jet can entrain flue gas inside the combustion chamber to dilute the concentrations of the fuel and oxygen. This is internal flue gas recirculation. Through such recirculation, the fuel and oxygen are diluted before combustion, thereby controlling the oxy-combustion flame temperature. Thermal NOx is also controlled through flue gas recirculation.

[0037] - The convection section 2 does not include utility units such as a boiling feed water economizer group and an ultra-high pressure steam superheater group configured to generate superheated steam. Only saturated steam 11 is generated from the transfer line exchanger. Therefore, the waste heat of the flue gas in the convection section 2 is only used to preheat the hydrocarbon feed and dilution steam.

[0038] Preferably, the diluent 3 can be steam. Alternatively, methane can be used as the diluent instead of steam. The mixture can also be superheated in the convection section 2. This is to ensure that the feed mixture no longer contains any droplets. The amount of superheat must be sufficient to exceed the dew point by a sufficient margin to prevent condensation of the diluent 3 or hydrocarbons. At the same time, decomposition of the feed and coke formation in the convection section 2 and in the transfer line exchanger where the risk of coke formation is still relatively high due to the higher temperature can be prevented. In addition, since the specific heats of the feed-diluent mixture 6 and the cracked gas 9 are very similar, the heat fluxes generated on both sides of the wall of the heat exchanger (i.e., the transfer line exchanger) are also similar. This means that the heat exchanger can operate with an almost identical temperature difference throughout the exchanger from the cold side to the hot side. This is advantageous from both a process and a mechanical perspective.

[0039] The combustion chamber may preferably be configured such that the combustion chamber efficiency is higher than 50%, preferably higher than 60%, more preferably higher than 70%. The combustion chamber efficiency is the ratio between the heat absorbed by at least one radiant coil 8 for converting the hydrocarbon feedstock 1 into cracked gas 9 by pyrolysis and the heat released by the combustion process. The normal combustion chamber efficiency of prior art cracking furnaces is about 40%. If we exceed this, the feedstock can no longer be heated to the optimum temperature because not enough heat is available in the flue gas: increasing the combustion chamber efficiency from about 40% to about 48% will reduce the proportion of heat available in the convection section 2 from about 50 - 55% to about 42 - 47%. Contrary to prior art systems, the system according to the invention can cope with this reduced availability of heat in the convection section 2. By increasing the combustion chamber efficiency by about 20% from about 40% to about 48%, about 20% of fuel can be saved. The combustion chamber efficiency can be increased in different ways, for example by increasing the adiabatic flame temperature in the combustion chamber and / or by increasing the heat transfer coefficient of at least one radiant coil 8.

[0040] At least one radiant coil 8 of the combustion chamber preferably comprises high - efficiency radiant tubes, such as swirl tubes as disclosed in EP1611386, EP2004320 or EP2328851, or winding ring radiant tubes as described in UK 1611573.5. More preferably, the at least one radiant coil 8 has an improved radiant coil layout, such as the three - channel layout as disclosed in US2008142411.

[0041] Another object of the present invention is to crack a hydrocarbon feedstock 1 in a cracking furnace system according to the present invention, the method comprising:

[0042] a) a feedstock pre - heating step in the convection section 2 at a temperature between 50°C and 180°C, preferably at a temperature between 150°C and 160°C,

[0043] b) a mixing step of mixing the hydrocarbon feedstock 1 pre - heated in step a) with a diluent 3 to form a feedstock - diluent mixture 6,

[0044] c) a pre - heating step of pre - heating the feedstock - diluent mixture 6 in a secondary transfer line exchanger 7 at a temperature between 250°C and 700°C, preferably at a temperature between 275°C and 500°C,

[0045] d) a cracking step of cracking the mixture pre - heated in step c) by combustion of oxygen or oxygen - enriched air 14 in the radiant section to produce cracked gas 9,

[0046] e) a first cooling step of cooling the cracked gas 9 in a primary transfer line exchanger (PTLE) 10,

[0047] f) A second cooling step of cooling the cracked gas 9 exiting the primary transfer line exchanger (PTLE) 10 in the secondary transfer line exchanger (STLE) 7, and

[0048] g) A generation step of generating saturated super-high pressure steam in the primary transfer line heat exchanger 10.

[0049] According to an embodiment, the method according to the present invention may include one or more of the following features:

[0050] - The saturated super-high pressure steam generated in step g) is generated from the water from the steam drum 12.

[0051] - The saturated super-high pressure steam generated in step g) is fed into the steam drum 12.

[0052] - The diluent 3 is dilution steam.

[0053] - The dilution steam is generated outside the cracking furnace system.

[0054] - Step d) includes a sub-step of controlling the combustion temperature in the radiant section by preferably diluting the fuel and oxygen or oxygen-enriched air 14 with internally recycled flue gas.

[0055] - The oxygen-enriched air contains more than 21% oxygen.

[0056] - In the cracking step d), flue gas is generated at a temperature between 950 °C and 1300 °C, preferably between 1000 °C and 1150 °C, and is sent to the convection section 2.

[0057] As Figure 1 shown, the cracking furnace system according to an embodiment of the present invention includes a convection section 2, and the convection section 2 includes a plurality of convection groups. The hydrocarbon raw material 1 can enter the feed preheater, which can be one of the plurality of convection groups in the convection section 2 of the cracking furnace system. The hydrocarbon raw material 1 can be any kind of hydrocarbon, preferably hydrocarbons of paraffinic or naphthenic nature, but a small amount of aromatics and olefins may also be present. Examples of such raw materials are: ethane, propane, butane, natural gasoline, naphtha, kerosene, natural condensate, gas oil, vacuum gas oil, hydrotreated or desulfurized or hydrodesulfurized (vacuum) gas oil or a combination thereof. The diluent 3, such as dilution steam, can also be preheated in the convection section 2. The preheated raw material 4 is mixed with the preheated diluent 5. The raw material / diluent mixture 6 is preheated in the secondary transfer line exchanger 7 to reach the optimum temperature for introduction into the radiant coil 8.

[0058] The radiant coil 8 can be, for example, a vortex type as disclosed in EP1611386, EP2004320 or EP2328851, or a three-channel radiant coil design (as disclosed in US2008 142411), or a wound loop type (UK1611573.5), or any other type that maintains a reasonable operating length, as known to those skilled in the art. In the radiant coil 8, the feed / diluent mixture 6 is rapidly heated to the point where the pyrolysis reaction begins, causing the hydrocarbon feed to be converted into products and by-products. Such products are especially hydrogen, ethylene, propylene, butadiene, benzene, toluene, styrene and / or xylene. The by-products are especially methane and fuel oil. The resulting mixture of diluent (such as dilution steam), unreacted feed and converted feed 9 (which is the reactor effluent known as "cracked gas") is rapidly cooled in the primary transfer line exchanger 10 and then rapidly cooled in the secondary transfer line exchanger 7 to freeze the reaction equilibrium in favor of the products. In a first inventive embodiment, the waste heat in the cracked gas 9 is first recovered in the primary transfer line exchanger 10 by generating saturated steam 11 from the water from the steam drum 12. The saturated steam 11 can be sent to the steam drum 12. The saturated super-high pressure is output 15.

[0059] In a second inventive embodiment, the waste heat in the cracked gas 9 is recovered a second time in the secondary transfer line exchanger 7 by heating the feed-diluent mixture 6 before sending it to the radiant coil 8.

[0060] As known to those skilled in the art, the heat of reaction for the highly endothermic pyrolysis reaction can be provided by burning fuel gas 13 in many different ways in the radiant section 18 (also known as the furnace combustion chamber). Oxygen or oxygen-enriched air 14 can be introduced, for example, directly into the burners of the furnace combustion chamber, where the fuel gas 13 and oxygen or oxygen-enriched air 14 are burned to provide the heat for the pyrolysis reaction. In the furnace combustion chamber, the fuel gas 13 and oxygen or oxygen-enriched air 14 are converted into combustion products, such as water and CO2, i.e., the so-called flue gas. The waste heat from the flue gas is recovered using various types of convection banks in the convection section 2. Part of the heat is used to preheat the hydrocarbon feed and / or diluent 3.

[0061] In summary, the present invention has the following advantages:

[0062] - The combustion oxidant can be pure oxygen or oxygen-enriched air 14. The inert gas present in the furnace is minimized without any additional inert gas injection or external recirculation.

[0063] - Oxy-fuel ethylene cracking has unique thermal integration. The convection section 2 consists only of the hydrocarbon feed and dilution steam preheating groups. The hydrocarbon feed and dilution steam mixture are further superheated against the cracking effluent in the transfer line feed effluent exchanger. Then the feed and dilution steam paths are directed to the radiant section for the cracking reaction.

[0064] - Remove the boiler feed water preheating and ultra-high pressure steam groups from the convection section 2. The boiler feed water is directly supplied to the steam drum 12. The saturated ultra-high pressure steam is output.

[0065] - Use oxy-fuel burners in the combustion chamber to transfer heat. The flue gas mass flow rate is reduced by more than 80%. The flue gas mainly contains carbon dioxide and water from combustion. Oxygen and fuel are staged in the oxy-fuel burners to control the heat flux distribution and NOx emissions.

Claims

1. A cracking furnace system for converting a hydrocarbon feedstock into cracked gas, the cracking furnace system comprising: A convection section; A radiation section; A cooling section, wherein the convection section includes a plurality of convection banks configured to receive only the hydrocarbon feedstock and a diluent, wherein the radiation section includes a combustion chamber, the combustion chamber including at least an oxygen or oxygen-enriched air burner and a plurality of radiant coils configured to heat the feedstock to a temperature allowing pyrolysis reaction, wherein the cooling section includes at least two transfer line exchangers (TLEs): a primary transfer line exchanger (PTLE) and a secondary transfer line exchanger (STLE), wherein the system further includes a mixing device configured and adapted to mix the preheated hydrocarbon feedstock and the preheated diluent, wherein the system is configured such that the hydrocarbon feedstock and diluent mixture is preheated in the secondary transfer line exchanger before entering the radiation section, wherein the primary transfer line exchanger is configured to generate saturated steam; And A steam drum connected to the primary transfer line exchanger.

2. The cracking furnace system according to claim 1, wherein the diluent is dilution steam.

3. The cracking furnace system according to claim 2, wherein the surface area of the radiant coils in the radiation section is formed by serpentine coils.

4. The cracking furnace system according to claim 1, wherein the cooling section includes a tertiary transfer line exchanger.

5. The cracking furnace system according to claim 1, wherein the radiation section includes an oxy-fuel burner.

6. The cracking furnace system according to claim 1, wherein the cracking furnace system includes a flame temperature control device in the radiation section.

7. The cracking furnace system according to claim 6, wherein the flame temperature control device includes a high-speed jet to introduce fuel and oxygen or oxygen-enriched air in the radiation section.

8. The cracking furnace system according to claim 1, wherein the convection section does not include common units such as a boiling feed water economizer bank and an ultra-high pressure steam superheater bank configured to generate superheated steam.

9. A method for cracking a hydrocarbon feedstock in a cracking furnace system, the method comprising: Preheating the feedstock in the convection section at a temperature between 50 °C and 180 °C; Mixing the preheated hydrocarbon feedstock with a diluent to form a mixed feedstock-diluent; Preheating the mixed feedstock-diluent in the secondary transfer line exchanger at a temperature between 250 °C and 700 °C; Cracking the preheated mixed feedstock-diluent by combustion of oxygen or oxygen-enriched air in the radiation section to produce cracked gas; Cooling the cracked gas in the primary transfer line exchanger (PTLE); Further cooling the cracked gas leaving the primary transfer line exchanger (PTLE) in the secondary transfer line exchanger (STLE); and Generating saturated ultra-high pressure steam in the PTLE.

10. The method according to claim 9, wherein the saturated ultra-high pressure steam is generated from water from the steam drum.

11. The method according to claim 9, wherein the generated saturated ultra-high pressure steam is fed into the steam drum.

12. The method according to claim 9, wherein the diluent is dilution steam.

13. The method according to claim 12, wherein the dilution steam is generated outside the cracking furnace system.

14. The method according to claim 9, wherein cracking the mixed feed-diluent comprises controlling the combustion temperature in the radiant section by diluting fuel and oxygen or oxygen-enriched air.

15. The method according to claim 9, wherein the oxygen-enriched air contains more than 21% oxygen.

16. The method according to claim 9, wherein cracking the mixed feed-diluent comprises generating flue gas at a temperature between 950 °C and 1300 °C and sending the flue gas to the convection section.

17. The method according to claim 16, wherein cracking the mixed feed-diluent comprises generating flue gas at a temperature between 1000 °C and 1150 °C.

18. The method according to claim 9, wherein preheating the feed in the convection section comprises preheating the feed in the convection section at a temperature between 150 °C and 160 °C.

19. The method according to claim 9, wherein preheating the mixed feed-diluent in the secondary transfer line exchanger comprises preheating the mixed feed-diluent in the secondary transfer line exchanger at a temperature between 275 °C and 500 °C.

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