CONTAINING HIGH BOILING COMPONENTS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/139,445, filed January 20, 2021, which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

[0002] The present invention generally relates to systems and methods for steam cracking hydrocarbons. More specifically, the present invention relates to a steam cracking system comprising a first steam cracking furnace and a second steam cracking furnace, and a process that uses the first steam cracking furnace to crack light components of a hydrocarbon feed and uses the second steam cracking furnace to crack heavy components of the hydrocarbon feed.

BACKGROUND OF THE INVENTION

[0003] Steam cracking is one of the most common processes for producing high valued chemicals including light olefins (C2 to C4 olefins) and BTX (benzene, toluene, and xylene). In the steam cracking process, hydrocarbons in a hydrocarbon and steam mixture are cracked in a steam cracker furnace via pyrolysis. The feedstocks of a steam cracker can be gaseous such as ethane, propane and butane, or liquid such as naphtha, gas condensate or gas oil.

[0004] In a steam cracking system, fouling and/or high coke formation often occur in the convection section, radiant section, and cooling section due to high percentage of hydrocarbons with high boiling points in the feed stream. To mitigate fouling and/or coke formation in the convection section of a steam cracking furnace, often the cracking conditions are adjusted. The adjustments can be, for example, a reduction of hydrocarbon flowrate or an increase of steam-to-oil ratio. This limits the amount of liquid in the convection section at high wall temperatures. As a result, the overall efficiency for steam cracking drops. A steamcracking furnace can typically be optimized for lighter liquid feedstocks (e.g. naphtha) or heavier feedstocks (e.g. gas oils). Therefore, the maximum allowable boiling point of these components of the feed stream is thus adjustable based on the parameters of the furnace. However, frequently, light feedstocks contain some high boiling components (e.g., heavy constituents of a gas condensate) and can either not be cracked in the furnace or require specific measures to prevent fouling in the convection section (e.g., higher steam to oil ratio, blending, etc.) of the steam cracker, increasing the operating cost for steam cracking. Furthermore, the optimal operating conditions of the steam cracking furnace, such as severity or coil outlet temperature, dilution steam ratio, flow, differ between light components and heavy components. Hence, optimizing operating conditions based on maximum boiling points of the feedstock can lead to a portion of the feedstock being processed under suboptimal reaction conditions, resulting in low selectivity or production efficiency for the overall steam cracking process.

[0005] Overall, while methods of steam cracking liquid hydrocarbon feedstocks exist, the need for improvements in this field persists in light of at least the aforementioned drawbacks for the methods.

BRIEF SUMMARY OF THE INVENTION

[0006] A solution to at least some of the above-mentioned problems with the method of steam cracking liquid hydrocarbon feedstocks has been discovered. The solution resides in a steam cracking system that includes separate furnaces, one of which is configured to steam crack light components and the other to steam crack heavy components of a liquid hydrocarbon. Notably, the liquid hydrocarbon feed stream is mixed with steam, and then processed in a vapor-liquid separation unit to produce a light vapor stream and a heavy stream. The light vapor stream is steam cracked in a radiant section of a first steam cracking furnace under first conditions optimized for light feedstocks. The heavy stream is further steam cracked in a second steam cracking furnace. This can be beneficial for at least increasing the overall steam cracking efficiency compared to conventional steam cracking processes by processing the light components and heavy components under their respective optimal conditions. Furthermore, the heavy stream comprising the heavy components is further vaporized before it is fed into radiant section of the second steam cracking furnace, thereby mitigating fouling and/or high coke formation rate caused by incomplete vaporization. Moreover, the vaporized heavy stream can be further separated in a vapor-liquid separation unit to separate out the heavy liquid components that are non-processable in the second radiant section, further reducing the fouling and/or coke formation in the radiant coils of the second steam cracking furnace. Additionally, the heavy stream can be pretreated to remove solids, sulfur, or other impurities before it is fed into the radiant section of the second steam cracking furnace, further mitigating the fouling of the radiant section. Therefore, the system and method of the present invention provide a technical solution to at least some of the problems associated with the conventional steam cracker and steam cracking process mentioned above.

[0007] Embodiments of the invention include a method of steam cracking hydrocarbons. The method comprises (a) heating a hydrocarbon feed stream in a first convection section of a first steam cracking furnace to a temperature sufficient to vaporize at least a portion of the hydrocarbon stream and form a heated hydrocarbon feed stream. The method comprises (b) mixing dilution steam with the heated hydrocarbon feed stream to produce a mixed feed stream. The method comprises (c) separating the mixed feed stream to form (i) a light vapor stream comprising steam and hydrocarbons in vapor phase and (ii) a heavy stream comprising liquid hydrocarbons. The method comprises (d) heating the light vapor stream of the first steam cracking furnace under first steam cracking conditions sufficient to crack the hydrocarbons of the light vapor stream.

[0008] Embodiments of the invention include a method of steam cracking hydrocarbons. The method comprises (a) heating a hydrocarbon feed stream in a first convection section of a first steam cracking furnace to a temperature sufficient to vaporize at least a portion of the hydrocarbon stream and form a heated hydrocarbon feed stream. The method comprises (b) mixing dilution steam with the heated hydrocarbon feed stream to produce a mixed feed stream. The method comprises (c) separating the mixed feed stream to form (i) a light vapor stream comprising steam and hydrocarbons in vapor phase and (ii) a heavy stream comprising liquid hydrocarbons. The method comprises (d) heating the light vapor stream in one or more radiant coils of the first steam cracking furnace under first steam cracking conditions sufficient to crack the hydrocarbons of the light vapor stream. The method comprises (e) heating the heavy stream in a second convection section of a second steam cracking furnace to produce a heated heavy stream. At least a portion of the heated heavy stream is in vapor phase. The method comprises (f) mixing the heated heavy stream with dilution steam to form a mixed heavy stream. The method comprises (g) heating at least a portion of the mixed heavy stream in one or more radiant coils of the second steam cracking furnace under second steam cracking conditions sufficient to crack the hydrocarbons of the mixed heavy stream. [0009] Embodiments of the invention include a method of steam cracking hydrocarbons. The method comprises (a) heating a hydrocarbon feed stream in a first convection section of a first steam cracking furnace to a temperature sufficient to vaporize at least a portion of the hydrocarbon stream and form a heated hydrocarbon feed stream. The method comprises (b) mixing dilution steam with the heated hydrocarbon feed stream to produce a mixed feed stream. The method comprises (c) separating the mixed feed stream to form (i) a light vapor stream comprising steam and hydrocarbons in vapor phase and (ii) a heavy stream comprising liquid hydrocarbons. The method comprises (d) heating the light vapor stream in one or more radiant coils of the first steam cracking furnace under first steam cracking conditions sufficient to crack the hydrocarbons of the light vapor stream. The method comprises pretreating the heavy stream in a pretreatment unit. The method further comprises (e) heating the heavy stream in a second convection section of a second steam cracking furnace to produce a heated heavy stream. At least a portion of the heated heavy stream is in vapor phase. The method comprises (f) mixing the heated heavy stream with dilution steam to form a mixed heavy stream. The method further comprises separating the mixed heavy stream into (I) a heavy vapor stream comprising steam and vaporized hydrocarbons, and (II) a heavy liquid stream comprising liquid hydrocarbons. The method comprises (g) heating at least a portion of the heavy vapor stream in one or more radiant coils of the second steam cracking furnace under second steam cracking conditions sufficient to crack the hydrocarbons of the mixed heavy stream.

[0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0012] The terms “wt.%”, “vol.%” or “mol.%” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component. [0013] The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0014] The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, include any measurable decrease or complete inhibition to achieve a desired result.

[0015] The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0016] The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0017] The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0018] The process of the present invention can “comprise,” “consist essentially of,” or “consist of’ particular ingredients, components, compositions, etc., disclosed throughout the specification.

[0019] The term “primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt.%, 50 mol.%, and 50 vol.%. For example, “primarily” may include 50.1 wt.% to 100 wt.% and all values and ranges there between, 50.1 mol.% to 100 mol.% and all values and ranges there between, or 50.1 vol.% to 100 vol.% and all values and ranges there between.

[0020] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0022] FIG. 1 shows a schematic diagram of a steam cracking system, according to embodiments of the invention;

[0023] FIG. 2A shows a schematic diagram of a first steam cracking furnace of a steam cracking system, according to embodiments of the invention;

[0024] FIG. 2B shows a schematic diagram of a second steam cracking furnace of a steam cracking system, according to embodiments of the invention; and

[0025] FIG. 3 shows a schematic flowchart of a method of steam cracking a hydrocarbon feed, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Currently, a steam cracker for steam cracking liquid hydrocarbon feedstocks generally comprises a single steam cracking furnace for both light and heavy components. Thus, in the convection section of a steam cracking furnace, often, at least some of the heavy components are not vaporized, resulting in fouling and/or coke formation in the convection section of the steam cracking furnace. Furthermore, both the light components and the heavy components are processed under the same steam cracking conditions in the radiant section of a conventional steam cracker, resulting in suboptimal process conditions for some of the components in the hydrocarbon feed stream. The present invention provides a solution to at least some of these problems. The solution is premised on a steam cracking system that comprises two steam cracking furnaces, one of which is configured to steam crack light components and the other to steam crack heavy components, respectively. Thus, light components and heavy components each can be processed under optimal conditions, resulting in increased steam cracking efficiency. Additionally, the disclosed steam cracking system includes a vapor-liquid separation unit to separate non-vaporized heavy components from a mixture of steam and vaporized hydrocarbon feed stream, thereby mitigating the fouling of the steam cracking furnaces. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. System for steam cracking hydrocarbons

[0027] In embodiments of the invention, the system for steam cracking liquid hydrocarbons comprises two steam cracking furnaces, a vapor-liquid separation unit in fluid communication with both steam cracking furnaces, optionally a pretreatment unit, and a cooling unit for each of the two steam cracking furnaces. With reference to FIG. 1, a schematic diagram is shown for system 100, which is capable of steam cracking hydrocarbons with mitigated furnace fouling and improved efficiency compared to conventional steam cracking systems.

[0028] According to embodiments of the invention, system 100 comprises first steam cracking furnace 101 comprising first convection section 102 and first radiant section 103. As shown in FIG. 2A, first convection section 102 comprises first feed preheater 104 configured to vaporize at least a portion of hydrocarbons in hydrocarbon feed stream 11 by heating. Hydrocarbon feed stream 11 may comprise naphtha, gas condensate, gas oil, diesel, crude oil or any renewable or circular hydrocarbon stream, or combinations thereof. In embodiments of the invention, an outlet of first feed preheater 104 is in fluid communication with a steam inlet such that an effluent stream of first feed preheater 104 is mixed with dilution steam stream 13 to form mixed feed stream 12.

[0029] According to embodiments of the invention, mixed feed stream 12 is fed into first vapor-liquid separation unit 105 configured to separate mixed feed stream 12 to produce (i) light vapor stream 14 comprising hydrocarbons in vapor phase and the steam from dilution steam stream 13, and (ii) heavy stream 15 comprising hydrocarbons in liquid phase (heavy components from hydrocarbon feed stream 11). First vapor-liquid separation unit 105 may include a flash drum, a knockout drum, a distillation column, a demister, or any combination thereof.

[0030] In embodiments of the invention, an outlet of first vapor-liquid separation unit 105 is in fluid communication with an inlet of first upper mixed preheater 106 such that light vapor stream 14 flows from first vapor-liquid separation unit 105 to first upper mixed preheater 106. First upper mixed preheater 106 may be in fluid communication with first lower mixed preheater 107 such that effluent from first upper mixed preheater 106 flows to first lower mixed preheater 107. In embodiments of the invention, first upper mixed preheater 106 and first lower mixed preheater 107 are operated in series. First upper mixed preheater 106 and/or first lower mixed preheater 107 may be configured to heat light vapor stream 14 to an inlet temperature for steam cracking.

[0031] According to embodiments of the invention, first radiant section 103 comprises one or more radiant coils 108 and first firebox 109 encompassing radiant coils 108. In embodiments of the invention, an outlet of first lower mixed preheater 107 may be in fluid communication with an inlet of radiant coil(s) 108 such that heated light vapor stream 14 flows from first lower mixed preheater 107 to radiant coil(s) 108. First radiant section 103 may be configured to heat light vapor stream 14 in radiant coil(s) 108 by first firebox 109 under first steam cracking conditions sufficient to crack at least a portion of hydrocarbons of light vapor stream 14 and produce first effluent stream 16 comprising cracked hydrocarbons. First firebox 109 may be configured to generate heat for heating radiant coil(s) via fuel combustion. According to embodiments of the invention, fuel combustion in first firebox 109 may produce flue gas, which can be used to provide heat for first convection section 102. In embodiments of the invention, an outlet of radiant coil(s) 108 is in fluid communication with first cooling unit 110 such that first effluent stream 16 flows from radiant coil(s) 108 to first cooling unit 110. First cooling unit 110 may be configured to cool first effluent stream 16 to a temperature such that reach on(s) or most reactions in first effluent stream 16 are stopped. In embodiments of the invention, first cooling unit 110 includes a transfer line exchanger, a shell and tube heat exchangers, a double pipe heat exchangers, a tube in tube heat exchangers, a quench oil injection unit, a water injection unit, a quenching tower, or any combination thereof.

[0032] According to embodiments of the invention, an outlet of first vapor-liquid separation unit 105 may be in fluid communication with pretreatment unit 111 such that heavy stream 15 flows from first vapor-liquid separation unit 105 to pretreatment unit 111. In embodiments of the invention, pretreatment unit I l l is configured to remove solids and/or impurities from heavy stream 15 to produce pretreated heavy stream 15'. Non-limiting examples of pretreatment unit 111 include a filtration unit, a cyclone based solid removal unit, a sulfur removal unit, a hydrotreating unit, a hydrocracking unit, an adsorption unit, or any combination thereof.

[0033] In embodiments of the invention, an outlet of pretreatment unit 111 is in fluid communication with an inlet of second steam cracking furnace 112 such that pretreated heavy stream 15' flows from pretreatment unit 111 to second steam cracking furnace 112. In embodiments of the invention, system 100 may not include pretreatment unit 111 and heavy stream may be flowed from an outlet of first vapor-liquid separation unit 105 to second steam cracking furnace 112 without pretreatment.

[0034] In embodiments of the invention, second steam cracking furnace 112 comprises second convection section 114 in fluid communication with second radiant section 115. According to embodiments of the invention, as shown in FIG. 2B, second convection section 114 comprises second feed preheater 116 configured to heat heavy stream 15 and/or pretreated heavy stream 15' to vaporize at least a portion of heavy stream 15 and/or pretreated heavy stream 15'. In embodiments of the invention, an outlet of second feed preheater 116 is in fluid communication with a steam inlet such that preheated heavy stream 15 (or pretreated heavy stream 15') mixes with dilution steam to form mixed heavy stream 17. In embodiments of the invention, mixed heavy stream 17 is fed into second vapor-liquid separation unit 117. Second vapor-liquid separation unit 117 may be configured to separate mixed heavy stream 17 into (I) heavy vapor stream 18 comprising vaporized hydrocarbons from heavy stream 15 and steam, and (II) heavy liquid stream 19 comprising liquid hydrocarbons from heavy stream 15.

[0035] According to embodiments of the invention, second convection section 114 of second steam cracking furnace 112 comprises second upper mixed preheater 118 and second lower mixed preheater 119 in series, configured to heat heavy vapor stream 18 to a second inlet temperature. In embodiments of the invention, second radiant section 115 includes second radiant coil(s) 120 and second firebox 121 encompassing second radiant coil(s) 120. Second firebox 121 may be configured to provide heat for second radiant coil(s) 120 via fuel combustion. Flue gas produced via fuel combustion in second firebox 121 may be used to provide heat for second convection section 114.

[0036] According to embodiments of the invention, second radiant section 115 is configured to heat heavy vapor stream 18 in second radiant coil(s) 120 under second steam cracking conditions sufficient to crack hydrocarbons in heavy vapor stream 18 to produce second effluent stream 20 comprising cracked hydrocarbons. In embodiments of the invention, an outlet of second radiant coil(s) 120 is in fluid communication with inlet of second cooling unit 122 such that second effluent stream 20 flows to second cooling unit 122. Second cooling unit 122 may be configured to cool second effluent stream 20 to a temperature such that reaction(s) in second effluent stream 20 is stopped. In embodiments of the invention, second cooling unit 122 includes transfer line exchanger, a quenching tower, a shell and tube heat exchanger, a double pipe heat exchanger, a tube in tube heat exchanger, a quench oil injection unit, a water injection unit, a quench tower, or combinations thereof. In embodiments of the invention, mixed heavy stream 17 may be directly fed into second upper mixed preheater 118 without being processed in second vapor-liquid separation unit 117 such that mixed heavy stream 17 is heated by second upper mixed preheater 118, second lower mixed preheater 119, and further cracked in second radiant section 115 to produce second effluent stream 20.

B. Method of steam cracking hydrocarbons

[0037] Methods for steam cracking hydrocarbons have been discovered. The hydrocarbons may include liquid hydrocarbons of naphtha, gas condensate, gas oil, diesel, crude oil, renewable or circular hydrocarbons, or combinations thereof. With reference to FIG. 3, a schematic flowchart is shown for method 200 for steam cracking hydrocarbons. Method 200 may be implemented by system 100, as shown in FIGS. 1, 2A and 2B, and described above.

[0038] According to embodiments of the invention, as shown in block 201 , method 200 comprises heating hydrocarbon feed stream 11 in first convention section 102 of first steam cracking furnace 101 to a temperature sufficient to vaporize at least a portion of hydrocarbon feed stream 11 and form heated hydrocarbon feed stream 11'. In embodiments of the invention, heating at block 201 is performed at first feed preheater 104. Hydrocarbon feed stream 11 may contain hydrocarbons with an initial boiling point of 30 to 300 °C and final boiling point of 300 to 500 °C. At block 201, hydrocarbon feed stream 11 may be heated to a temperature in a range of 100 to 400 °C.

[0039] According to embodiments of the invention, as shown in block 202, method 200 comprises mixing dilution steam of dilution steam stream 13 with heated hydrocarbon feed stream 11 to produce mixed feed stream 12. In embodiments of the invention, at block 202, heated hydrocarbon feed stream 11 and dilution steam stream 13 are mixed at a volumetric ratio of from 0.1 to 2.0 and all ranges and values there between including ranges of 0.1 to 0.2, 0.2 to 0.4, 0.4 to 0.6, 0.6 to 0.8, 0.8 to 1.0, 1.0 to 1.2, 1.2 to 1.4, 1.4 to 1.6, 1.6 to 1.8, and 1.8 to 2.0. In embodiments of the invention, prior to mixing at block 202, dilution steam is at a temperature of 180 to 600 °C including ranges of 180 to 210 °C, 210 to 240 °C, 240 to 270 °C, 270 to 300 °C, 300 to 330 °C, 330 to 360 °C, 360 to 390 °C, 390 to 420 °C, 420 to 450 °C, 450 to 480 °C, 480 to 510 °C, 510 to 540 °C, 540 to 570 °C, and 570 to 600 °C.

[0040] According to embodiments of the invention, as shown in block 203, method 200 comprises separating, in first vapor-liquid separation unit 105, mixed feed stream 12 to form (i) light vapor stream 14 comprising steam and hydrocarbons in vapor phase and (ii) heavy stream 15 comprising liquid hydrocarbons. In embodiments of the invention, separating at block 203 is performed at a temperature of 100 to 400 °C and a pressure of 3 to 15 bar. In embodiments of the invention, hydrocarbons of light vapor stream 14 may have a boiling range of 30 to 350 °C. Hydrocarbons of heavy stream 15 may have a boiling range of 150 to 500 °C. In embodiments of the invention, as shown in block 204, method 200 includes heating light vapor stream 14 in first upper mixed preheater 106 and/or first lower mixed preheater 107. At block 204, light vapor stream 14 may be heated to a temperature in a range of 500 to 700 °C and all ranges and values there between including ranges of 500 to 520 °C, 520 to 540 °C, 540 to 560 °C, 560 to 580 °C, 580 to 600 °C, 600 to 620 °C, 620 to 640 °C, 640 to 660 °C, 660 to 680 °C, and 680 to 700 °C.

[0041] According to embodiments of the invention, as shown in block 205, method 200 includes heating light vapor stream 14 in one or more radiant coils 108 of first radiant section 102 of first steam cracking furnace 101 under first steam cracking conditions sufficient to crack the hydrocarbons of light vapor stream 14. In embodiments of the invention, first steam cracking conditions include first cracking temperature of 750 to 900 °C and all ranges and values there between including ranges of 750 to 760 °C, 760 to 770 °C, 770 to 780 °C, 780 to 790 °C, 790 to 800 °C, 800 to 810 °C, 800 to 810 °C, 810 to 820 °C, 820 to 830 °C, 830 to 840 °C, 840 to 850 °C, 850 to 860 °C, 860 to 870 °C, 870 to 880 °C, 880 to 890 °C, and 890 to 900 °C. First steam cracking conditions may further include first residence time of 100 to 1000 ms and all ranges and values there between including ranges of 100 to 200 ms, 200 to 300 ms, 300 to 400 ms, 400 to 500 ms, 500 to 600 ms, 600 to 700 ms, 700 to 800 ms, 800 to 900 ms, and 900 to 1000 ms. In embodiments of the invention, first effluent stream 16 from first radiant coil(s) 108 may include light olefins (C2 to C4 olefins) and/or BTX (benzene, toluene, xylene). At block 205, hydrocarbons of light vapor stream 14 may be cracked to generate a propylene to ethylene weight ratio (PZE ratio) in a range of 0.1 to 0.9 and all ranges and values there between including ranges of 0.1 to 0.2, 0.2 to 0.3, 0.3 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, and 0.8 to 0.9.

[0042] According to embodiments of the invention, as shown in block 206, method 200 includes optionally pretreating heavy stream 15 in pretreatment unit 111 to form pretreated heavy stream 15'. In embodiments of the invention, the pretreating at block 206 includes solid removal in a filtration unit and/or a cyclone unit, and/or sulfur removal in a sulfur removal unit. In embodiments of the invention, pretreatment unit 111 is used to pretreat heavy components (boiling points over 150 °C) from other steam cracking furnaces.

[0043] According to embodiments of the invention, as shown in block 207, method 200 comprises heating heavy stream 15 or pretreated heavy stream 15' in second convection section 114 of second steam cracking furnace 112 to produce heated heavy stream 22. Heating at block 207 may be performed in second feed preheater 116. In embodiments of the invention, at least a portion of heated heavy stream 22 is in vapor phase. Heated heavy stream 22 may be at a temperature in a range of 150 to 500 °C and all ranges and values there between including ranges of 150 to 200 °C, 200 to 250 °C, 250 to 300 °C, 300 to 350 °C, 350 to 400 °C, 400 to 450 °C, and 450 to 500 °C.

[0044] According to embodiments of the invention, as shown in block 208, method 200 comprises mixing heated heavy stream 22 with dilution steam to form mixed heavy stream 17. In embodiments of the invention, mixed heavy stream 17 includes a hydrocarbon to steam volumetric ratio in a range of 0.1 to 2.0 and all ranges and values there between including ranges of 0.1 to 0.2, 0.2 to 0.4, 0.4 to 0.6, 0.6 to 0.8, 0.8 to 1.0, 1.0 to 1.2, 1.2 to 1.4, 1.4 to 1.6, 1.6 to 1.8, and 1.8 to 2.0. In embodiments of the invention, prior to mixing at block 208, dilution steam is at a temperature of 180 to 600 °C and all ranges and values there between including ranges of 180 to 210 °C, 210 to 240 °C, 240 to 270 °C, 270 to 300 °C, 300 to 330 °C, 330 to 360 °C, 360 to 390 °C, 390 to 420 °C, 420 to 450 °C, 450 to 480 °C, 480 to 510 °C, 510 to 540 °C, 540 to 570 °C, and 570 to 600 °C.

[0045] According to embodiments of the invention, as shown in block 209, method 200 comprises separating mixed heavy stream 17 in second vapor-liquid separation unit 117 to form (I) heavy vapor stream 18 comprising steam and vaporized hydrocarbons, and (II) heavy liquid stream 19 comprising liquid hydrocarbons. In embodiments of the invention, separating at block 209 is conducted at a temperature of 150 to 500 °C and a pressure of 3 to 15 bar. Hydrocarbons of heavy vapor stream 18 may have a boiling range of 150 to 500 °C and all ranges and values there between including ranges of 150 to 200 °C, 200 to 250 °C, 250 to 300 °C, 300 to 350 °C, 350 to 400 °C, 400 to 450 °C, and 450 to 500 °C. Hydrocarbons of heavy liquid stream 19 may have a boiling range of greater than 300 °C. In embodiments of the invention heavy liquid stream 19 may be subjected to further processing, including a hydrotreating unit, a hydrocracking unit, an adsorption unit, or combinations thereof. In embodiments of the invention, as shown in block 210, method 200 may include heating heavy vapor stream 18 in second upper mixed preheater 118 and second lower mixed preheater 119. In embodiments of the invention, at block 210, heavy vapor stream 18 may be heated to a temperature of 550 to 750 °C and all ranges and values there between including ranges of 550 to 570 °C, 570 to 590 °C, 590 to 610 °C, 610 to 630 °C, 630 to 650 °C, 650 to 670 °C, 670 to 690 °C, 690 to 710 °C, 710 to 730 °C, and 730 to 750 °C.

[0046] According to embodiments of the invention, as shown in block 211, method 200 comprises heating at least a portion of mixed heavy stream 17 (which can be heavy vapor stream 18) in one or more radiant coils 120 of second radiant section 115 of second steam cracking furnace 112 under second steam cracking conditions sufficient to crack the hydrocarbons of the at least a portion mixed heavy stream 17. In embodiments of the invention, the second steam cracking conditions include second cracking temperature of 750 to 900 °C and all ranges and values there between including ranges of 750 to 760 °C, 760 to 770 °C, 770 to 780 °C, 780 to 790 °C, 790 to 800 °C, 800 to 810 °C, 810 to 820 °C, 820 to 830 °C, 830 to 840 °C, 840 to 850 °C, 850 to 860 °C, 860 to 870 °C, 870 to 880 °C, 880 to 890 °C, and 890 to 900 °C. Second steam cracking conditions may include second residence time of 100 to 1000 ms and all ranges and values there between including ranges of 100 to 200 ms, 200 to 300 ms, 300 to 400 ms, 400 to 500 ms, 500 to 600 ms, 600 to 700 ms, 700 to 800 ms, 800 to 900 ms, and 900 to 1000 ms. In embodiments of the invention, second effluent stream 20 from second radiant coil(s) may include light olefins (C2 to C4 olefins) and/or BTX (benzene, toluene, xylene). At block 211, hydrocarbons of heavy vapor stream 18 may be cracked to produce a propylene to ethylene ratio (PZE ratio) in a range of 0.1 to 0.9 and all ranges and values there between including ranges of 0.1 to 0.2, 0.2 to 0.3, 0.3 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, and 0.8 to 0.9. [0047] In embodiments of the invention, as shown in block 212, method 200 can include heating mixed heavy stream 17 in second upper mixed preheater 118 and second lower mixed preheater 119 without separating step at block 209. According to embodiments of the invention, at block 212, mixed heavy stream 17 may be heated to a temperature of 150 to 500 °C and all ranges and values there between including ranges of 150 to 200 °C, 200 to 250 °C, 250 to 300 °C, 300 to 350 °C, 350 to 400 °C, 400 to 450 °C, and 450 to 500 °C.. As shown in block 213, method 200 may include steam cracking the heated mixed heavy stream in second radiant coil(s) 120 of second radiant section 115 under third steam cracking conditions to produce an effluent stream of the second radiant coil(s) 120 comprising steam cracked hydrocarbons. The effluent stream of second radiant coil(s) 120 can include light olefins (C2 to C4 olefins) and/or BTX (benzene, toluene, xylene). The third steam cracking conditions may include a third cracking temperature of 750 to 900 °C and third residence time of 100 to 1000 ms.

[0048] Although embodiments of the present invention have been described with reference to blocks of FIG. 3, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 3. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 3.

[0049] The systems and processes described herein can also include various equipment that is not shown and is known to one of skill in the art of chemical processing. For example, some controllers, piping, computers, valves, pumps, heaters, thermocouples, pressure indicators, mixers, heat exchangers, and the like may not be shown.

[0050] As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLE

(Simulations of a Steam Cracking Process)

[0051] Simulations of steam cracking processes were conducted in SPYRO and Aspen+. In these simulations, the systems used for steam cracking were as shown in FIGS. 1, 2A (first steam cracking furnace), and 2B (second steam cracking furnace). Steam cracking in a conventional steam cracking system was simulated as control. For the first steam cracking furnace, a flash vessel was used as the liquid-vapor separation unit. The flash vessel was operated at a fixed temperature of 230 °C. The properties of the feed stream, light end (the components that is vaporized to form light vapor stream), and heavy stream are shown in Table 1. The operating conditions of the steam cracking system are shown in Table. 2.

Table 1. Properties of the feed stream, light vapor stream, and heavy stream

Table 2. Operating conditions of steam cracking system [0052] The flow rate of the feed stream fed into the furnace was set to 50 t/hr, resulting in a flow rate of 43 t/hr for the light end (light vapor stream) and 7 t/hr for the heavy stream for the disclosed steam cracking system. In the second steam cracking furnace, the heavy streams of several light furnaces (furnaces substantially the same as the first steam cracking furnace) was combined to form a heavy stream with a flow rate of 45 t/hr. The highest wall temperatures at which liquid was observed in the first steam cracking furnace was about 266 °C while in the second steam cracking furnace (for processing heavy stream) had a highest wall temperature with liquid hydrocarbons at 314 °C. This was surprisingly and significantly lower than that of a conventional furnace, even though only limited optimization was performed. In a conventional furnace with a similar design as the first steam cracking furnace without the vapor-liquid separation unit, the highest wall temperature with liquid hydrocarbons for the same feed stream was 340 °C. The lower wall temperatures in the first and second steam cracking furnace than the conventional steam cracking furnace indicate lower the risk of fouling compared to the conventional steam cracking furnace, which was configured to process the whole feed stream. It was also found that the invention opens up several optimization parameters that can improve operations efficiency of the steam cracking system in terms of energy and yields. Soft parameters that can be optimized (besides the design of the furnace) include, for example, the coil outlet temperature of each furnace, feed flow rates to each furnace, dilution steam ratio of each furnace, dilution steam temperature of each furnace. To reduce fouling for using the feed stream, the conventional furnace would have to increase the temperature of dilution steam. In embodiments of the invention, only the second furnace requires higher temperatures of dilution steam and only a limited amount is required in comparison to the conventional furnace (114 t/hr vs. 45 t/hr). Further optimization of the furnaces and operating conditions is possible to improve these results as well as optimize yields and energy consumption of the respective furnaces.

[0053] In the context of the present invention, at least the following 14 embodiments are described. Embodiment 1 is a method of steam cracking hydrocarbons. The method includes: (a) heating a hydrocarbon feed stream in a first convection section of a first steam cracking furnace to a temperature sufficient to vaporize at least a portion of the hydrocarbon feed stream and form a heated hydrocarbon feed stream; (b) mixing dilution steam with the heated hydrocarbon feed stream to produce a mixed feed stream; (c) separating the mixed feed stream to form (i) a light vapor stream comprising steam and hydrocarbons in vapor phase and (ii) a heavy stream comprising liquid hydrocarbons; and (d) heating the light vapor stream in the first steam cracking furnace under first steam cracking conditions sufficient to crack the hydrocarbons of the light vapor stream. Embodiment 2 is the method of embodiment 1, further including: (e) heating the heavy stream in a second convection section of a second steam cracking furnace to produce a heated heavy stream, wherein at least a portion of the heated heavy stream is in vapor phase; (f) mixing the heated heavy stream with dilute steam to form a mixed heavy stream; and (g) heating at least a portion of the mixed heavy stream in one or more radiant coils of the second steam cracking furnace under second steam cracking conditions sufficient to crack the hydrocarbons of the mixed heavy stream. Embodiment 2 is the method of embodiment 2, further including, prior to step (e), pretreating the heavy stream in a pretreatment unit. Embodiment 4 is the method of embodiment 3, wherein the pretreatment unit includes a filtration unit, a cyclone based solid removal unit, a sulfur removal unit, or combinations thereof. Embodiment 5 is the method of any of embodiments 2 to 4, further including, prior to step (g), separating the mixed heavy stream to form (I) a heavy vapor stream comprising steam and vaporized hydrocarbons, and (II) a heavy liquid stream comprising liquid hydrocarbons. Embodiment 6 is the method of any of embodiments 2 to 5, wherein the second steam cracking conditions include a reaction temperature in a range of 750 to 900 °C. Embodiment 7 is the method of any of embodiments 2 to 6, wherein the second steam cracking conditions include a residence time of the second steam cracking furnace in a range of 100 to 1000 ms. Embodiment 8 is the method of any of embodiments 2 to 7, wherein, in step (e), the heavy stream is heated to a temperature of 150 to 500 °C. Embodiment 9 is the method of any of embodiments 2 to 8, further including, prior to step (g), heating at least a portion of heavy mixed stream to a temperature of 500 to 700 °C. Embodiment 10 is the method of any of embodiments 1 to 9, wherein the first steam cracking conditions include a reaction temperature in a range of 750 to 900 °C. Embodiment 11 is the method of any of embodiments 1 to 10, wherein the first steam cracking conditions include a residence time of the first steam cracking furnace in a range of 100 to 1000 ms. Embodiment 12 is the method of any of embodiments 1 to 11, wherein the dilute steam is at a temperature of 180 to 600 °C. Embodiment 13 is the method of any of embodiments 1 to 12, wherein, in step (a), the hydrocarbon feed stream is heated to a temperature of 100 to 400 °C. Embodiment 14 is the method of any of embodiments 1 to 12, further including, prior to step (d), heating at least a portion of light vapor stream to a temperature of 500 to 700 °C.

[0054] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.