Pyrolysis furnace processing of contaminated feedstocks

Abstract

Disclosed is a process that includes flowing a hydrocarbon material through a first tube bank disposed in a convection section of a pyrolysis furnace along a flow path of a flue gas generated in a radiant section of the pyrolysis furnace. The process further includes flowing the hydrocarbon material through a second tube bank disposed upstream of the first tube bank along the flow path of the flue gas. Then, the process includes flowing the hydrocarbon material through a third tube bank disposed downstream of the second tube bank along the flow path of the flue gas. Flowing the hydrcarbon material through the second tube bank before the third tube bank may prevent non-volatile material deposition in areas of the convection where it is difficult to remove the non-volatile material deposits.

Description

PYROLYSIS FURNACE PROCESSING OF CONTAMINATED FEEDSTOCKSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 678,312 having a filing date of August 01, 2024, the disclosure of which is incorporated herein by reference in its entirety.FIELD

[0002] This disclosure relates to pyrolysis furnaces and processing of hydrocarbon material with pyrolysis furnaces. In particular, this disclosure relates to processes and pyrolysis furnaces for processing hydrocarbon materials that include contaminants which may otherwise result in fouling in pyrolysis furnaces. The devices and processes of this disclosure are especially useful for reducing fouling and removing heavy molecules, such as coke, tar, asphaltenes, ash, char, and the like, from a convectional section of a steam cracking furnace.BACKGROUND

[0003] Crude oils and fractions thereof are typically processed first by fractionating in a refinery and then by cracking, such as in a pyrolysis furnace to yield various products including light olefins, such as ethylene, propylene, and butylene.

[0004] Conventional steam cracking utilizes a pyrolysis furnace which has two main sections: a convection section and a radiation section. In operation, the feedstock enters the convection section of the furnace where it is heated and, in the case of a liquid-phase feed, vaporized by indirect contact with hot flue gas from the radiant section and combined with steam. The vaporized feedstock and steam mixture is then introduced into the radiant section where the cracking takes place. The resulting products, including the valuable light olefins (e.g., ethylene, propylene, and butylene), leave the pyrolysis furnace for further downstream processing, including quenching and recovery using one or more fractionating columns or towers, caustic treatment, washing, or reactors.

[0005] The liquid feedstock is generally selected such that fouling of the convection section does not occur. As referred to herein, “fouling” refers to the formation of deposits (e.g., nonvolatile material) of heavy molecules, such as coke, tar, asphaltenes, PAHs, solids entrained in the feed, and several other sources, including ash and char within the convection section that negatively affect the pyrolysis furnace performance due to increased pressure drop, reduced heat transfer and plugging, and other problems in tube banks of the convection section.

[0006] In general, hydrocarbon materials that include asphaltenes and other heavy molecules (e.g., high final boiling point (FBP) materials or materials contaminated with polyaromatic hydrocarbons (PAH)s, ash, char, or other solids or semi-solids) are not used as feedstocks because the asphaltenes and / or other heavy molecules become convection section fouling precursors. For example, materials derived from plastic waste may include contaminants, such as ash, char, coke, PAHs, asphaltenes, long polymer chains, or other solids or semi solids, that can foul the convection section. Further, materials such as condensates and naphthas may be contaminated by asphaltenic molecules or PAHs, and / or have a high FBP. For instance, condensates and naphthas are often transported in containers, such as ships, which have previously contained crude oil, heavy gas oil, residual oils (e.g., resids and / or residuum), and the like, having FBP greater than 950°F (510°C) and small but significant amounts of material having FBP of 1200°F (650°C) and higher. Condensates may also be obtained from the gasfields contaminated with these high FBP molecules. Once contaminated, these materials have decreased value as pyrolysis furnace feeds because they may result in fouling or coking within the convection section. In any case, a range of hydrocarbon materials are not used in current pyrolysis sections or, if used, may increase the rate at which a pyrolysis section should receive maintenance.

[0007] References of interest include U.S. Patent Nos. 7,297,833 and 7,625,480, and PCT Application Nos. PCT / US2009044586 (WO 2010 / 005633A1) and PCT / US2020 / 023737 (WO 2020191253A1).SUMMARY

[0008] This disclosure relates to a process that includes (I) flowing a hydrocarbon material through a first tube bank disposed in a convection section of a pyrolysis furnace along a flow path of a flue gas generated in a radiant section of the pyrolysis furnace, wherein the first tube bank transfers heat between the flue gas and the hydrocarbon material. The process also includes (II) adding water and / or steam to the hydrocarbon material inside or outside of the convection section. Further, the process includes (III) after step (I), flowing the hydrocarbon material through a second tube bank disposed in the convection section of the pyrolysis furnace along the flow path of the flue gas, wherein the second tube bank transfers heat between the flue gas and the hydrocarbon material. Further still, the process includes (IV) after step (III), flowing the hydrocarbon material through a third tube bank disposed in the convection section of the pyrolysis furnace along the flow path of the flue gas, wherein the third tube bank transfers heat between the flue gas and the hydrocarbon material. Further still, the process includes (V) flowing the hydrocarbon material from the convection section to the radiant section of the pyrolysis furnace to steam crack the hydrocarbon stream to generate a stream cracked effluent. Even further, the process includes (VI)sequentially contacting the flue gas with the second tube bank, the third tube bank, and the first tube bank along the flow path of the flue gas.

[0009] The disclosure also relates to a system. The system includes a pyrolysis furnace having a convection section and a radiant section, the convection section having a section length along a flow path of a flue gas generated in a radiant section of the pyrolysis furnace. Further, the system includes a first tube bank, a second tube bank, and a third tube tank located in the convection section, each configured to flow a hydrocarbon material therethrough and to transfer heat between the flue gas and the hydrocarbon material. Further still, the system includes an inlet for receiving water and / or steam into the hydrocarbon material. The first tube bank is upstream of the second tube bank, and the second tube bank is upstream of the third tube bank, in the flow path of the hydrocarbon material flowing therethrough. Further, the second tube bank is disposed upstream of the third tube bank along the flow path of the flue gas. Further still, the third tube bank is disposed upstream of the first tube bank along the flow path of the flue gas.

[0010] These and other features and attributes of the disclosed pyrolysis furnace and convection section of the present disclosure and their advantageous applications and / or uses will be apparent from the detailed description which follows.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] To assist those of ordinary skill in the relevant art in making and using the subject matter hereof, reference is made to the appended drawings, wherein:

[0012] FIG. 1 is a schematic diagram of a pyrolysis furnace that includes a convection section and a radiant section, in accordance with an aspect of the present disclosure;

[0013] FIG. 2 is a schematic diagram of a first example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure;

[0014] FIG. 3 is a schematic diagram of a second example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure;

[0015] FIG. 4 is a schematic diagram of a third example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure;

[0016] FIG. 5 is a schematic diagram of a fourth example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure;

[0017] FIG. 6 is a schematic diagram of a fifth example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure; and

[0018] FIG. 7 is a schematic diagram of a sixth example of the convection section of the pyrolysis furnace of FIG. 1, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0019] One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0020] When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. All numerical values within the detailed description herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art. For example, “about” or “approximately” may indicate that an amount may be ± 0.5%, ±1 %, ± 2%, ± 5%, or ± 10% the amount.

[0021] In this disclosure, a process is described as including at least one “step.” It should be understood that each step is an action or operation that may be carried out once or multiple times in the process, in a continuous or discontinuous fashion. Unless specified to the contrary or the context clearly indicates otherwise, multiple steps in a process may be conducted sequentially in the order as they are listed, with or without overlapping with one or more other steps, or in any other order, as the case may be. In addition, one or more or even all steps may be conducted simultaneously with regard to the same or different batch of material. For example, in a continuous process, while a first step in a process is being conducted with respect to a raw material just fed into the beginning of the process, a second step may be carried out simultaneously with respect to an intermediate material resulting from treating the raw materials fed into the process at an earlier time in the first step. Preferably, the steps are conducted in the order described.

[0022] The term “hydrocarbon” as used herein means (i) any compound consisting of hydrogen and carbon atoms or (ii) any mixture of two or more such compounds in (i). The term “Cn hydrocarbon,” where n is a positive integer, means (i) any hydrocarbon compound comprising carbon atom(s) in its molecule at the total number of n, or (ii) any mixture of two or more such hydrocarbon compounds in (i). Thus, a C2 hydrocarbon can be ethane, ethylene, acetylene, ormixtures of at least two of these compounds at any proportion. A “Cm to Cn hydrocarbon” or “Cm-Cn hydrocarbon,” where m and n are positive integers and m < n, means any of Cm, Cm+1, Cm+2, ..., Cn-1, Cn hydrocarbons, or any mixtures of two or more thereof. Thus, a “C2 to C3 hydrocarbon” or “C2-C3 hydrocarbon” can be any of ethane, ethylene, acetylene, propane, propene, propyne, propadiene, cyclopropane, and any mixtures of two or more thereof at any proportion between and among the components. A “saturated C2-C3 hydrocarbon” can be ethane, propane, cyclopropane, or any mixture thereof of two or more thereof at any proportion. A “Cn+ hydrocarbon” means (i) any hydrocarbon compound comprising carbon atom(s) in its molecule at the total number of at least n, or (ii) any mixture of two or more such hydrocarbon compounds in (i). A “Cn- hydrocarbon” means (i) any hydrocarbon compound comprising carbon atoms in its molecule at the total number of at most n, or (ii) any mixture of two or more such hydrocarbon compounds in (i). A “Cm hydrocarbon stream” means a hydrocarbon stream consisting essentially of Cm hydrocarbon(s). A “Cm-Cn hydrocarbon stream” means a hydrocarbon stream consisting essentially of Cm-Cn hydrocarbon(s).

[0023] The terms “resid” and “residuum” refer to a bottoms cut of a crude distillation process that contains non-volatile components. Resids are complex mixtures of heavy petroleum compounds otherwise known in the art as residuum or residual or pitch. Atmospheric resid is the bottoms product produced from atmospheric distillation of crude where a typical endpoint of the heaviest distilled product is nominally 343°C, and is referred to as 343°C resid. The term “nominally”, as used herein, means that reasonable experts may disagree on the exact cut point for these terms, but by no more than + / - 55.6°C preferably no more than + / - 27.8°C. Vacuum resid is the bottoms product from a distillation column operated under vacuum where the heaviest distilled product can be nominally 566°C, and is referred to as 566°C resid.

[0024] The term “hydrocarbon feed” or “hydrocarbon material” refers to a composition that includes one or more hydrocarbons. Illustrative hydrocarbon feeds can be or can include, but are not limited to, crude, gas oils, heating oil, jet fuel, diesel, kerosene, gasoline, coker naphtha, steam cracked naphtha, catalytically cracked naphtha, hydrocrackate, reformate, raffinate reformate, Fischer-Tropsch liquids and / or gases, natural gasoline, distillate, virgin naphtha, atmospheric pipestill bottoms, vacuum pipestill streams such as vacuum pipestill bottoms and wide boiling range vacuum pipestill naphtha to gas oil condensates, non-virgin hydrocarbons from refineries, vacuum gas oils, heavy gas oil, naphtha contaminated with crude, atmospheric residue, heavy residue, a C residue admixture, naphtha / residue admixture, hydrocarbon gases / residue admixture, hydrogen / residue admixtures, waxy residues, gas oil / residue admixture, relatively light alkanes, e.g., ethane, propane, butane, and / or pentane, recycle streams that can include ethane,propane, ethylene, propylene, butadiene, or a mixture thereof, one or more condensates, fractions thereof, or any mixture thereof.

[0025] The term “coke” refers to the solid or semi-solid product that can be produced during the steam cracking of hydrocarbons that includes carbon and high carbon-content organic molecules, whether produced within the convection section, radiant section, transfer lines therebetween, or within transfer lines and other equipment, e.g., a transfer line heat exchanger, downstream of the radiant section.

[0026] As referred to herein, a “naphtha” refers to a material obtainable as a distillate of petroleum with a boiling range of approximately 70 to 400 °F (20 to 205°C).

[0027] The term “asphaltene” refers to a material obtainable from crude oil or other sources and having an initial boiling point above 650°C and which is insoluble in a paraffinic solvent. At least in some instances, asphaltenes may include waxes, heavy oils, and resins, which may be measured using ASTM D3279 Asphaltene Content & Heptane Insolubles.

[0028] It is noted that some types of plastic material can also include bio-derived components. For example, some types of plastic labels can include biogenic waste in the form of paper compounds. In some embodiments, 1 wt% to 25 wt% of the plastic material of a pre- or postconsumer plastic feedstock material can correspond to bio-derived material. Such bio-derived material can also potentially contribute to the nitrogen content and / or oxygen content of a plastic material. The plastic material, in addition to the one or more polymers, can also include any additives, modifiers, packaging dyes, and / or other components typically added to a polymer during and / or after formulation. The plastic material can also further include any components typically found in polymer waste. In some embodiments, the plastic material may include a liquid material.

[0029] A "polymer" has two or more of the same or different repeating units / mer units or simply units. A "homopolymer" is a polymer having repeating units that are the same. A "copolymer" is a polymer having two or more repeating units that are different from each other. As such, the term “copolymer” includes terpolymers (a polymer having three units that are different from each other), tetrapolymers (a polymer having four units that are different from each other), and so on. The term "different" as used to refer to units indicates that the units differ from each other by at least one atom and / or are different isomerically.

[0029] In some embodiments, the polymer can be or can include, but is not limited to, a nitrogen-containing polymer, a chlorine-containing polymer, a bromine-containing polymer, a fluorine-containing polymer, an oxygen-containing polymer, a polyethylene polymer, a polypropylene polymer, a polystyrene polymer, a butadiene polymer, an isoprene polymer, anisobutylene polymer, or any mixture thereof. In some embodiments, the oxygen-containing polymer can be or can include a polyterephthalate polymer, an ethylene vinyl acetate polymer, a polycarbonate polymer, a polylactic acid polymer, an acrylate polymer, a polyoxymethylene polymer, a polyester polymer, a polyoxybenzylmethylenglycolanhydride polymer, a polyepoxide polymer, or any mixture thereof. In some embodiments, the nitrogen-containing polymer can be or can include one or more polyamide polymers, e.g., nylon; one or more polynitrile polymers, e.g., poly(acrylonitrile) and / or poly(methacrylonitrile); one or more aramids, one or more polyurethane polymers, or any mixture thereof.

[0030] In this disclosure, a polymer that includes both oxygen and nitrogen as part of the repeat unit for forming the polymer is defined as a nitrogen-containing polymer for purposes of characterizing the plastic feedstock. In some embodiments, the chlorine-containing polymers can be or can include, but are not limited to, polyvinyl chloride (PVC) and / or polyvinylidene chloride (PVDC). A polymer can be naturally occurring, modified naturally occurring, and / or synthetic.

[0031] The plastic material alone, the plastic material that has been processed, through chemical reactions, solvation, or other processes, or the plastic material mixed, blended, or otherwise combined with an optional carrier liquid is also referred to as a “heavy feed.” Although the heavy feed may have a similar or identical composition as the hydrocarbon feed, preferably the heavy feed differs from the hydrocarbon feed. Although the hydrocarbon feed may contain a plastic material, e.g., the same or different plastic material contained in the heavy feed, preferably the hydrocarbon feed is substantially free, or completely free of a plastic material. Preferably, the hydrocarbon feed is derived from a petroleum source substantially free or completely free of a plastic material.

[0032] The terms “char” and “ash” interchangeably refer to the solid, solid / liquid mixture, or semisolid produced during the pyrolysis of an optionally contaminated plastic material and deposited on the inner surface of a conduit or vessel, which can include organic molecules having long carbon chains and / or high boiling points such as asphaltenes, coke, organometallic compounds, inorganic materials such as metals, metallic oxides, and salts, organometallic molecules, and mixtures thereof. Char and ash may be produced from the chemical reactions of the various components of a plastic material and / or introduced directly from the plastic feed material.

[0033] An "olefin" is a linear, branched, and / or cyclic compound (e.g., certain cyclic molecules are branched) of carbon and hydrogen having at least one double bond. The term “olefin product” as used herein means a product that includes an olefin, preferably a product consisting essentially of or consisting of an olefin. An olefin product in the meaning of this disclosure can be, e.g., anethylene stream, a propylene stream, a butylene stream, an ethylene / propylene mixture stream, and the like.

[0034] The term “aromatic” as used herein is to be understood in accordance with its art- recognized scope which includes alkyl substituted and unsubstituted mono- and poly-nuclear compounds.

[0035] All ranges expressed herein should include both end points as two specific embodiments unless specified or indicated to the contrary.

[0036] As discussed above, many hydrocarbon materials (e.g., hydrocarbon feeds) may include contaminants, such as asphaltenes, condensates, naphtha, ash, char, relatively large molecules (e.g., long polymer chains or PAHs), and other materials that may foul the convection section of the pyrolysis furnace. For example, certain industrial practices to use plastic waste that include contaminants involve significantly diluting the contaminated hydrocarbon materials with carrier feeds, such that relatively low fractions (e.g., less than or equal to 1 percent by weight (wt%), less than or equal to 5 wt%, or less than or equal to 10 wt%) of the total feed to the steam cracking furnace includes the contaminants. However, mixing such heavy carrier feeds with plastic waste limits the rate of plastic waste entering the pyrolysis furnace, and thus reduces the rate of processing of the plastic waste. Furthermore, cracking the heavy carrier feeds may increase costs associated with operating the pyrolysis furnace. Accordingly, it is presently recognized that there is a need to improve the diversity of feedstock while also limiting negative effects, such as increased costs, reduced throughput, and other negative effects.

[0037] Accordingly, the present disclosure is directed to techniques for processing a variety of hydrocarbon materials by selectively depositing coke and other non-volatilizing materials in particular locations within the pyrolysis furnace. In general, the techniques include directing a hydrocarbon material with water and / or steam to a tube bank disposed in an upstream section of a convection section and subsequently directing the hydrocarbon material with water and / or steam to a tube bank disposed in a downstream section (e.g., relative to the direction of hot flue gas that flows from the radiant section and around the tube banks) of the convection section. For example, a convection section of a pyrolysis furnace may include at least three tube banks. Further, the tube banks are arranged such that the hydrocarbon material flows sequentially from a first tube bank to a second tube bank, and from the second tube bank to a third tube bank. The tube banks are arranged such that a flue gas generated in pyrolysis section sequentially contacts the second tube bank, the third tube bank, and the first tube bank. It is presently recognized that heating a hydrocarbon material such that when the majority (>90%) of the hydrocarbon stream vaporizes, any non-volatilizing material deposit (e.g., non-volatile material or heavy molecules, such as coke,tar, asphaltenes, PAHs, solids entrained in the feed, and several other sources, including ash and char) within a lower portion of the convection section (e.g., less than 50%, 40%, 30%, 20%, or 10% of the height of the convection section, or between 50% and 20%, between 40% and 20%, between 30% and 10% of the height of the convection section) will enable a broader range of feedstock to be used in pyrolysis furnace. As described herein, the height of the convection section may refer to a total number of convection rows.

[0038] Reference is now made to the embodiments illustrated in FIGS. 1-7 wherein like numerals are used to designate like parts throughout.

[0039] FIG. 1 shows a schematic diagram of an embodiment of a pyrolysis furnace 10 in accordance with the present disclosure. As shown, the pyrolysis furnace 10 includes a convection section 12 and a radiant section 14. The convection section 12 generally receives a hydrocarbon material 16 (e.g., a feedstock in accordance with aspects of the present disclosure) and, while within the convection section 12 (e.g., one or more tube banks within the convection section 12), the hydrocarbon material 16 is heated and vaporized by indirect contact with a hot flue gas 18 emitted by or generated in a combustion zone 19 having one or more burners 20 in the radiant section 14 (e.g., via one or more burners). Water and / or steam 21 is added to the hydrocarbon material 16 to form a mixture 17. The mixture 17, which may include vaporized hydrocarbon material 16, is ultimately directed into the radiant section 14. The water and / or steam 21 may be added to the hydrocarbon material 16 inside or outside of the convection section 12.

[0040] As shown in the illustrated embodiment, the convection section 12 includes a first tube bank 22, a second tube bank 24, and a third tube bank 26. The first tube bank 22, the second tube bank 24, and the third tube bank 26 are arranged along the longitudinal axis 28 of the pyrolysis furnace 10. Put differently, the first tube bank 22, the second tube bank 24, and the third tube bank 26 are located at different longitudinal positions along the section height 30 of the convection section 12. In the illustrated embodiment, the first tube bank 22, the second tube bank 24, and the third tube bank 26 are aligned about the center of each tube bank. Each tube bank 22, 24, and 26 includes one or more tubes extending through the interior of the pyrolysis furnace 10 across a flow path of the hot flue gas 18. The hot flue gas 18 contacts an exterior of the one or more tubes of each tube bank 22, 24, and 26, whereas the hydrocarbon material 16 contacts and flows within an interior (e.g., internal flow path) of the one or more tubes of each tube bank 22, 24, and 26. The one or more tubes of each tube bank 22, 24, and 26 may wind back and forth across the flow path of the hot flue gas 18 to improve heat transfer between the hot flue gas 18 and the hydrocarbon material 16. In general, each tube bank 22, 24, and 26 may include any number (e.g., an odd number or even number) of tubes (e.g., 2, 3, 4, 5, 6, or more than 6) and having any suitable size.Moreover, each tube bank 22, 24, and 26 may include any suitable heat transfer profiling (e.g., ability to transfer heat from the flue gas 18). Further, while the illustrated embodiment shows the tubes of the tube banks 22, 24, and 26 running down the longitudinal axis 28 and along a width of the convection section 12, it should be noted that the tubes of the tube banks 22, 24, and 26 may also extend along a depth (into the page) of the convection section 12. In operation, the hydrocarbon material 16 flows into the first tube bank 22 (e.g., via an inlet 22a of the first tube bank 22). The number of rows in each tube bank 22, 24, and 26 may be influenced by the routing requirements of connecting pipe(s) between banks.

[0041] Within the first tube bank 22, the hydrocarbon material 16 is heated to a first temperature via heat exchange between the flue gas 18 and the first tube bank 22. As discussed in more detail below, the first temperature may be within a threshold range below the dewpoint of the mixture 17 (e.g., no greater than about 60°C, 50°C, 40°C, 30°C, 20°C, 15°C, 10°C, 5°C, 2°C, or 1°C below the dewpoint). For example, the mixture 17 may be heated to a first temperature, Tl, where Td - 60°C < Tl < Td, and where Td is the dewpoint of the mixture 17 (e.g., at an entry to the second tube bank 24) in an embodiment where the threshold range is no greater than 60°C below the dewpoint of the mixture 17.

[0042] The first tube bank 22 is fluidly coupled to the second tube bank 24 (e.g., via a fluid conduit connecting an outlet 22b of the first tube bank 22 and an inlet 24a of the second tube bank 24). The water and / or steam 21 is mixed with the hydrocarbon material 16 upstream of the second tube bank 24 to form the mixture 17. As such, during operation, the hydrocarbon material 16 flows from the first tube bank 22 to the second tube bank 24. Within the second tube bank 24, the mixture 17 is heated to a second temperature via heat exchange between the flue gas 18 and the second tube bank 24. As discussed in more detail below, the second temperature may be a temperature sufficient to vaporize at least a portion (e.g., greater than about 90%, greater than about 95%, greater than about 99%) of the hydrocarbon material 16 in the mixture 17 within the second tube bank 24. In preferred embodiments, the second temperature may be a temperature sufficient to vaporize about 100% of the hydrocarbon material 16 in the mixture 17 within the second tube bank 24. The second tube bank 24 is fluidly coupled to the third tube bank 26 (e.g., via a fluid conduit connecting an outlet 24b of the second tube bank 24 and an inlet 26a of the third tube bank 26). As such, during operation, the mixture 17 flows from the second tube bank 24 to the third tube bank 26. Within the third tube bank 26, the mixture 17 is heated to a third temperature via heat exchange between the flue gas 18 and the third tube bank 26. In general, the third temperature may be a temperature suitable for efficient cracking of the hydrocarbon material 16 that is mixed with steam 21 (e.g., the mixture 17).

[0043] In the illustrated embodiment, the second tube bank 24 is upstream of the third tube bank 26 relative to a flow direction of the flue gas 18 along the longitudinal axis 28. Further, the third tube bank 26 is upstream of the first tube bank 22 relative to the flow direction of the flue gas 18 along the longitudinal axis 28. In other words, the third tube bank 26 is disposed longitudinally between the first tube bank 22 and the second tube bank 24 along the longitudinal axis 28. As such, the flue gas 18 contacts the second tube bank 24 before the flue gas 18 contacts the third tube bank 26, and the flue gas 18 contacts the third tube bank 26 before the flue gas 18 contacts the first tube bank 22. Therefore, when the hydrocarbon material 16 is within the second tube bank 24, the hydrocarbon material 16 transfers heat with a relatively higher temperature of flue gas 18 as compared to the temperature of the flue gas 18 when the flue gas 18 contacts the third tube bank 26 and the first tube bank 22. Further, the first tube bank 22, the second tube bank 24, and the third tube bank 26 are fluidly coupled (e.g., via fluid conduits), such that the hydrocarbon material 16 flows sequentially through the first tube bank 22, the second tube bank 24, and then the third tube bank 26 (e.g., in a series arrangement).

[0044] In some embodiments, the hydrocarbon material 16 may include hydrocarbon and contaminants. In some embodiments, the hydrocarbon material 16 is at least partially derived from plastic. For example, at least 1%, at least 2%, at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99% of the hydrocarbon material may be derived from plastic based on the total weight of the hydrocarbon material 16. In some embodiments, less than 1% (e.g., or a concentration corresponding to a maximum or threshold dilution) of the hydrocarbon material may be derived from plastic based on the total weight of the hydrocarbon material 16. In some embodiments, the hydrocarbon material 16 includes one or more of C5s, naphtha, condensates, gas oils, and other heavy fractions of crude oil that may or may not have been processed or refined. In some embodiments, the hydrocarbon material 16 may include contaminants such as asphaltenes.

[0045] In conventional pyrolysis furnaces, a feedstock is directed along tube banks such that the feedstock is subjected to a flue gas at gradually increasing temperatures. However, it is presently recognized that it may be advantageous to flow mixture 17 through a tube bank heated by a flue gas 18 of a relatively higher temperature before flowing the hydrocarbon material through a tube bank heated by a flue gas 18 of a relatively lower temperature (e.g., alternating low, high, and low temperatures in tube banks 22, 24, and 26). In particular, it is noted that heating the mixture 17 with flue gas 18 at a position substantially closer to the radiant section 14 may preferentially or selectively cause deposition of a nonvolatile material (e.g., coke) at a lower portion 29 (e.g., lowersection) of the convection section 12. In particular, it is relatively easier to de-coke (e.g., remove coking and other deposits a tube bank when the deposit forms in a tube bank within the lower portion 29 of the convection section 12. For example, and referring back to FIG. 1, the lower portion 29 of the convection section 12 where it may be advantageous to form the deposit may be at position that is at 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, or 15% or less of the section height 30 of the convection section 12 closest to the radiant section 14 (e.g., immediately downstream of the radiant section 14 in the flow direction of the flue gas 18). As discussed herein, the section height 30 may be represented or measured using a total number of convection rows within the convection section 12. In this way, the illustrated embodiment routes the mixture 17 to the lower portion 29 of the section height 30 of the convection section 12 that corresponds to the second tube bank 24, thereby preferentially or selectively causing any deposits to form in a region of the convection section 12 where it is easier to decoke. Accordingly, hydrocarbon material 16 including contaminants that form deposits may be used by the pyrolysis furnace 10, because the deposits may advantageously form in the regions of the convection section 12 where it is easier to decoke.

[0046] Furthermore, it is presently recognized that it may be beneficial to preheat the hydrocarbon material 16 within the first tube bank 22 to a particular temperature range before the hydrocarbon material flows through the lower portion 29. In general, it is presently recognized that it may be beneficial to preheat a mixture 17 including the hydrocarbon material 16 to within a temperature range below the dewpoint of the mixture 17 of the hydrocarbon material 16 with the steam 21 and / or water at the inlet 24a to the second tube bank 24. At least in some instances, it may be beneficial to preheat the mixture 17 to within a temperature range or limit below the dewpoint of the mixture 17 at the lowermost bank (e.g., at the inlet 24a to the second tube bank 24 described herein, as compared to the outlet of the first tube bank 22). For example, the temperature range that the mixture 17 is heated to below the first tube bank 22 (e.g., at the inlet 24a) may be no higher than (e.g., at least equal to or less than) about 60°C, 50°C, 40°C, 30°C, 20°C, 19°C, 18°C, 17°C, 16°C, 15°C, 14°C, 13°C, 12°C, 11°C, 10°C, 5°C, 2°C, or 1°C below the dewpoint of the mixture 17.

[0047] After heating the mixture 17 in the first tube bank 22, the mixture 17 may be directed to the second tube bank 24. In general, the second tube bank 24 is disposed within the lower portion 29 of the section height 30 of the convection section 12 of the pyrolysis furnace 10 where it may be advantageous to form a deposit, as discussed herein. It is presently recognized that it is advantageous to heat the mixture 17 within the second tube bank 24 such that at least a portion of the hydrocarbon material 16 is vaporized. For example, it may be advantageous to heat themixture 17 such that between 75% to 100% of the hydrocarbon is vaporized and supplied to the third tube bank 26. For example, it may be advantageous to heat the hydrocarbon material such that at least 75%, at least 80%, at least 85%, at least 90%, at least 95% of the hydrocarbon material16 and / or the mixture 17 is vaporized when the mixture 17 is supplied to the third tube bank 26. In preferred embodiments, it may be advantageous to fully vaporize the hydrocarbon material 16 within the mixture 17 in the second tube bank 24. In preferred embodiments, it may be advantageous to heat the mixture 17 such that only a vapor is supplied to the third tube bank 26. By vaporizing a relatively large amount of hydrocarbon material 16 within the mixture 17, the third tube bank 26 may not receive a substantial portion of the hydrocarbon material 16 that may form a deposit (e.g., a nonvolatile material that remains within the tubes after vaporization of the hydrocarbon material, which may, in some instances, form coke) within a less desirable portion of the convection section 12 (e.g., outside or downstream of the lower portion 29 in the flow direction of the flue gas 18). Further, in some instances, a deposit may form on the third tube bank 26. However, the quantity of deposit on the internal surface of the third tube bank 26 may be no more than 20%, 10%, 5%, or less than 5% of a quantity of the deposit on an internal surface of the second tube bank 24. For example, a first quantity of deposit in the third tube bank 26 may be 20%, 10%, 5%, or less than 5% relative to a second amount of deposit in the second tube bank 24.

[0048] It should be noted that convection section 12 fouling in any service, inclusive of pyoil, is the result of nonvolatile components, which are defined as ash, char, asphaltenes, coke, and other organic, metallic, or organometallic components of pyoil which do not vaporize where >99% of the total liquid flow is already vapor before the exit of the convection section 12. Nonvolatile components, at least in some instances, may cause a pyrolysis furnace to operate in an unexpected or undesirable manner, such as by fouling or tube plugging within the convection section. As such, in some instances, it is preferred that all the hydrocarbon material 16 within the mixture 17 be volatilized in the lower portion 29 of the convection section 12 such that any deposits may be removed with an online or offline decoke operation. For example, each of the tube banks 22, 24, and 26 may include rows of horizontal tubes extending crosswise (i.e., perpendicular into the page) relative to the longitudinal axis 28 at different axial positions along the longitudinal axis 28. In such an embodiment, it may be desirable that all of the hydrocarbon material 16 within the mixture17 be volatilized in lower portion 29 where it may be easier to remove deposits via decoking interval or decoking operation, as described below.

[0049] In some embodiments, the pyrolysis furnace 10 may be operated in a decoking interval. As referred to herein, a “decoking interval” or a “decoking operation” refers to an operation of thepyrolysis furnace 10 where the pyrolysis furnace 10 is heated to a temperature and / or fluids (e.g., steam, oxidizers, air, or a combination thereof) are provided to the tube banks to oxidize and remove any deposits (e.g., of cokes or other organic materials as discussed herein) within the radiant section 14 and remove some portion of any non-organic deposits. Further, “online decoking” refers to steam and / or water decoking, and “offline decoking” refers to steam-air decoking. Both methods of decoking (e.g., online and offline) may clean the convection section 12 when the deposits form in the lower portion 29, as described herein, and reduce or eliminate the need of mechanical cleaning of the convection section 12. At least in some instances, during a decoking operation, the air / steam decoking mixture is hot enough to burn the deposits, thereby removing the deposits from the convection section 12. As described herein, the disclosed embodiments may promote coke and other deposits to deposit in the second tube bank 24 as opposed to the third tube bank 26, which is located downstream of the second tube bank 24 along the flow path of the flue gas 18. As such, the second tube bank 24 may receive the flue gas 18 at a relatively higher temperature, which may facilitate the decoking operation because the temperature in the lower portion 29 may have a sufficiently high temperature for removing deposits.

[0050] As shown in the illustrated embodiment, the convection section 12 and the radiant section 14 may be inline, or stacked vertically. That is, the center of the convection section 12 and the radiant section 14 are coaxial along the section height 30. However, in some embodiments, the convection section 12 and the radiant section 14 may be offset about the section height 30. That is, the center of the convection section 12 may be at a first position along the transverse axis 35, and the center of the radiant section 14 may be at a second position along the transverse axis 35 that is different than the first position.

[0051] The illustrated embodiment of the convection section 12 also includes a steam preheating tube bank 32 and an auxiliary tube bank 34. In general, the steam preheating tube bank 32 may preheat the water and / or steam 21. For example, steam 21 and / orwater may be superheated before injecting the steam 21 into the hydrocarbon material 16 to form the mixture 17. Alternatively, any water may be heated to form steam 21, before the fluid (e.g., water, steam, water and steam, or only water) is injected into the hydrocarbon material 16. The temperature of the mixture 17 including the steam 21 and hydrocarbon material 16 may be between approximately 30 to approximately 340°C. To illustrate this, FIG. 2 is a schematic diagram of a first example of the convection section 12 in accordance with certain embodiments of the present disclosure. As shown, the convection section 12 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, and the steam preheating tube bank 32 arranged along the section height 30.As illustrated, the steam preheating tube bank 32 is disposed downstream of the third tube bank 26 and upstream of the first tube bank 22 along the longitudinal axis 28 relative to the flow of the flue gas 18. In general, the hydrocarbon material 16 or mixture 17 moves sequentially through the first tube bank 22, the second tube bank 24, the third tube bank 26. The flue gas 18 sequentially contacts the second tube bank 24, the third tube bank 26, and the first tube bank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the second tube bank 24, to the third tube bank 26, and to the first tube bank 22. In any case, after leaving the radiant section 14, the cracked hydrocarbon material 16 may be sent to a downstream processing system 36.

[0052] As shown in the illustrated embodiment, the water and / or steam 21 is added to the hydrocarbon material 16 upstream (e.g., relative to the flow of the hydrocarbon material 16) of the second tube bank 24 or before the hydrocarbon material 16 flows into the second tube bank 24. However, in some embodiments, the water and / or steam 21 is added to the hydrocarbon material 16 after the hydrocarbon material 16 flows into the second tube bank 24.

[0053] In the illustrated embodiment of FIG. 2, a mixing hydrocarbon 40 is mixed with the hydrocarbon material 16. Accordingly, the mixture 17 may also include the mixing hydrocarbon 40. In general, the mixing hydrocarbon 40 may be any hydrocarbon material, including crudebased paraffinic material and / or may be asphaltene-free hydrocarbon with a boiling point exceeding 350°C. For example, in a preferred embodiment, the hydrocarbon material is asphaltene-free. The amount of mixing hydrocarbon 40 may be a suitable amount to raise the final boiling point of the hydrocarbon material to greater than 350°C, greater than 360°C, greater than 370°C, greater than 380°C, greater than 390°C, greater than 400°C, greater than 410°C, greater than 420°C, greater than 450°C, greater than 480°C, or greater than 500°C. In some embodiments, the mixing hydrocarbon 40 may be a high boiling point hydrocarbon that has a higher boiling point than a boiling point or average boiling point of the hydrocarbon material 16. As such, the mixing hydrocarbon 40 may reduce the possibility of deposits forming at higher sections within the convection section 12. The quantity of mixing hydrocarbon 40 to be added will be an amount sufficient to raise the final boiling point of the hydrocarbon material 16, which can be determined by routine experimentation by one of ordinary skill in the art in possession of the present disclosure. The final boiling point (FBP) of the hydrocarbon material 16 and mixing hydrocarbon 40 composite may be defined utilizing the terminology for FBP from ASTM methods D2887, D7096, D7169 as the point at which 99.5% of the cumulative area and / or volume count is eluted from the chromatogram or alternatively utilizing a) the definition in D86 as the maximum corrected thermometer reading obtained during the test or b) the definition from DI 160 as the maximum vapor temperature reached during the test. This may be further aided by vapor / liquidsimulations using commercially available software, such as AVEVA PRO / II™ that is now available from AVEVA, previously available from Schneider Electric and Simulation Sciences Inc.

[0054] In some embodiments, the mixing hydrocarbon 40 may be added to the hydrocarbon material 16 after the hydrocarbon material 16 at least partially flows through the first tube bank 22. To illustrate this, FIG. 3 is a schematic diagram of a second example of the convection section 12 in accordance with certain embodiments of the present disclosure. Similar to the convection section 12 described in FIG. 2, the illustrated embodiment of FIG. 3 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, and the steam preheating tube bank 32 arranged along the section height 30. As illustrated, the steam preheating tube bank 32 is disposed downstream of the third tube bank 26 and upstream of the first tube bank 22 along the longitudinal axis 28 and relative to the flow of the flue gas 18. However, in this illustrated embodiment, the mixing hydrocarbon 40 is added to the first tube bank 22. For example, the mixing hydrocarbon40 may be added at a position that is within a lower portion (e.g., 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10 or less) of the tube bank height41 of the first tube bank 22, wherein the lower portion of the tube bank height 41 is the portion of the first tube bank 22 closest to the radiant section 14 relative to the flow direction of the flue gas 18 along the longitudinal axis 28. In general, the hydrocarbon material 16 or mixture 17 moves sequentially through the first tube bank 22, the second tube bank 24, the third tube bank 26. The flue gas 18 sequentially contacts the second tube bank 24, the third tube bank 26, and the first tube bank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the second tube bank 24, to the third tube bank 26, and to the first tube bank 22.

[0055] In some embodiments, the convection section 12 may include multiple auxiliary tube banks 34. The auxiliary tube banks 34 may include tube banks that do not provide a flow path for the hydrocarbon material 16, but otherwise utilize the heat from the flue gas 18 to heat other fluids (e.g., water and / or steam). To illustrate this, FIG. 4 is a schematic diagram of a third example of the convection section 12 in accordance with certain embodiments of the present disclosure. As shown, the convection section 12 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, the steam preheating tube bank 32, and two auxiliary tube banks 34 arranged along the section height 30. As illustrated, the steam preheating tube bank 32 is disposed downstream of the third tube bank 26 and upstream of the first tube bank 22 along the longitudinal axis 28 and relative to the flow of the flue gas 18. In general, the hydrocarbon material 16 moves sequentially through the first tube bank 22, the second tube bank 24, the third tube bank 26. The flue gas 18 sequentially contacts the second tube bank 24, the third tube bank 26, and the first tubebank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the second tube bank 24, to the third tube bank 26, and to the first tube bank 22.

[0056] The two auxiliary tube banks 34 include a boiler water preheat tube bank 42 (e.g., an economizer) and a steam bank 44, which may include high- or super-high-pressure steam. The high-pressure (HP) steam may have a pressure greater than about 150 psia. In general, the boiler water preheat tube bank 42 may receive water 46 and preheat it for use with a steam drum or other component that utilizes steam or water. For example, the steam bank 44 may superheat steam 48 to form a high-pressure steam. In some embodiments, the steam bank 44 may receive a desuperheater water 47 that may be the used to control the temperature of the superheat steam 48. As shown, the boiler water preheat tube bank 42 is downstream of the first tube bank 22 along the flow path of the flue gas 18 (e.g., substantially parallel to the longitudinal axis 28). However, it should be noted that the boiler water preheat tube bank 42 may be disposed in other suitable positions within the convection section 12, such as upstream of the first tube bank 22.

[0057] As shown, the steam bank 44 is disposed downstream of the second tube bank 24 along the flow path of the flue gas 18 (e.g., substantially parallel to the longitudinal axis 28). However, it should be noted that the steam bank 44 may be disposed in other suitable positions within the convection section 12, such as downstream of the third tube bank 26. To illustrate this, FIG. 5 is a schematic diagram of a fourth example of the convection section 12 in accordance with certain embodiments of the present disclosure. As shown, the convection section 12 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, the steam preheating tube bank 32, and two auxiliary tube banks 34 (e.g., the boiler water preheat tube bank 42 and the high-pressure steam bank 44) arranged along the section height 30. As illustrated, the boiler water preheat tube bank 42 is disposed downstream of the first tube bank 22 relative to the flow of the flue gas 18. Accordingly, the boiler water preheat tube bank 42 may be heated by a flue gas 18 that has a relatively lower temperature than the first tube bank 22 in this embodiment. Accordingly, FIGS. 4 and 5 generally illustrate the multiple tube banks (e.g., the steam preheating tube bank 32 and / or auxiliary tube banks 34) for functions other than heating the hydrocarbon material 16 or mixture 17 that may be utilized in accordance with the present disclosure. In general, the hydrocarbon material 16 moves sequentially through the first tube bank 22, the second tube bank 24, the third tube bank 26. The flue gas 18 sequentially contacts the second tube bank 24, the third tube bank 26, and the first tube bank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the second tube bank 24, to the third tube bank 26, and to the first tube bank 22.

[0058] In some embodiments, the hydrocarbon material 16 may be directed to an additional tube bank after exiting the third tube bank 26. For example, it may be advantageous to further heat thehydrocarbon material 16 before the hydrocarbon material 16 flows to the radiant section 14. To illustrate this, FIG. 6 is a schematic diagram of a fifth example of the convection section 12 in accordance with certain embodiments of the present disclosure. As shown, the convection section 12 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, and the steam preheating tube bank 32 arranged along the section height 30. Additionally, the convection section 12 includes a fourth tube bank 50. In general, the hydrocarbon material 16 moves sequentially through, the first tube bank 22, the second tube bank 24, the third tube bank 26, and the fourth tube bank 50. The flue gas 18 sequentially contacts the fourth tube bank 50, the second tube bank 24, the third tube bank 26, and the first tube bank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the fourth tube bank 50, to the second tube bank 24, to the third tube bank 26, and to the first tube bank 22.

[0059] The convection section 12 in the illustrated embodiment generally runs in a similar operation as described with respect to FIG. 1. For example, the first tube bank 22 is fluidly coupled to the second tube bank 24, and the second tube bank 24 is fluidly coupled to the third tube bank 26. As such, the hydrocarbon material 16 (e.g., mixed with the mixing hydrocarbon 40) flows sequentially from the first tube bank 22 to the second tube bank 24 to the third tube bank 26.

[0060] As discussed above, it may be advantageous to further heat the hydrocarbon material 16 before the hydrocarbon material 16 flows to the radiant section 14. Accordingly, the fourth tube bank 50 may be utilized. In particular, and as shown, the fourth tube bank 50 is fluidly coupled to the third tube bank 26 (e.g., via a fluid conduit connecting an outlet of the third tube bank 26 and an inlet 50a of the fourth tube bank 50). As such, during operation, the hydrocarbon material 16 flows from the third tube bank 26 to the fourth tube bank 50. Within the fourth tube bank 50, the hydrocarbon material 16 is heated to a fourth temperature via heat exchange between the flue gas 18 and the fourth tube bank 50. In general, the fourth temperature may be a temperature suitable for efficient cracking of the hydrocarbon material 16 that is mixed with steam 21 that may not be reached within the third tube bank 26 since the third tube bank 26 is disposed at a relatively more upstream position along the longitudinal axis 28 due to the presence of the second tube bank 24.

[0061] In certain examples above, the hydrocarbon material 16 is shown leaving the second tube bank 24 at a relatively lower row than the row where the hydrocarbon material 16 entered the second tube bank. In some instances, the hydrocarbon material 16 may flow co-currently through the second tube bank 24 with the direction of flow of the flue gas 18. That is, the hydrocarbon material 16 may flow sequentially through rows of a tube bank (e.g., the second tube bank 24, thethird tube bank 26, the fourth tube bank 50, or a combination thereof) from a relatively lower section (e.g., along the section height 30) to a relatively higher section. FIG. 7 is a schematic diagram of a fourth example of the convection section 12 in accordance with certain embodiments of the present disclosure. As shown, the convection section 12 includes the first tube bank 22, the second tube bank 24, the third tube bank 26, the steam preheating tube bank 32, and two auxiliary tube banks 34 (e.g., the boiler water preheat tube bank 42 and the high-pressure steam bank 44) arranged along the section height 30. As illustrated, the boiler water preheat tube bank 42 is disposed downstream of the first tube bank 22. Accordingly, the boiler water preheat tube bank 42 may be heated by a flue gas 18 that has a relatively lower temperature than the first tube bank 22 in this embodiment. In general, the hydrocarbon material 16 moves sequentially through the first tube bank 22, the second tube bank 24, the third tube bank 26. The flue gas 18 sequentially contacts the second tube bank 24, the third tube bank 26, and the first tube bank 22. Accordingly, the temperature of the flue gas 18 may decrease sequentially from the second tube bank 24, to the third tube bank 26, and to the first tube bank 22. In particular, the hydrocarbon material 16 and / or the steam 21 enter the second tube bank 24 at the lowest row along the section height 30.

[0062] Accordingly, the present disclosure relates to techniques for heating hydrocarbon material 16, such that a deposit preferentially forms in a lower portion 29 of the convection section 12 of a pyrolysis furnace 10 where it may be relatively easier to decoke. In general, it is presently recognized that the lower portion 29 (e.g., between 10% to 50%, between 20% to 50%, between 25% to 50% of the section height 30) of the convection section 12 may have a temperature suitable for facilitating the decomposition of coke deposits. For example, the hydrocarbon material 16 may be directed to a tube bank disposed in a first location of the convection section 12, and subsequently directed to a tube bank disposed in a second location of the convection section 12 that is upstream along the flow path of the flue gas 18 heating the tube banks. It is presently recognized that the disclosed techniques may provide several advantages over existing pyrolysis furnaces. For example, the pyrolysis furnace may be operated in an online or offline decoking of the convection section 12 to remove coke deposits (e.g., formed in the second tube bank 24) without relatively long downtime of the pyrolysis furnace 10. Further, the disclosed techniques (e.g., the arrangement of the tube banks) may cause any non-volatile materials to deposit in regions of the convection section 12 that are exposed to higher temperatures, thereby presenting an advantage over convention furnaces where non-volatile material may deposit higher in the convection section. As such, a broader range of feedstocks may be utilized, including those with contaminants and pyoil with little to no dilution of the feedstock. In this way, the disclosed techniques provide more efficient techniques for operation pyrolysis furnaces.

[0063] This written description uses embodiments / examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other embodiments / examples that occur to those skilled in the art. Such other embodiments / examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Many alterations, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description without departing from the spirit or scope of the present disclosure and that when numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims

CLAIMS:

1. A process, comprising:(I) flowing a hydrocarbon material through a first tube bank disposed in a convection section of a pyrolysis furnace along a flow path of a flue gas generated in a radiant section of the pyrolysis furnace, wherein the first tube bank transfers heat between the flue gas and the hydrocarbon material;(II) adding water and / or steam to the hydrocarbon material inside or outside of the convection section;(III) after step (I), flowing the hydrocarbon material through a second tube bank disposed in the convection section of the pyrolysis furnace along the flow path of the flue gas, wherein the second tube bank transfers heat between the flue gas and the hydrocarbon material;(IV) after step (III), flowing the hydrocarbon material through a third tube bank disposed in the convection section of the pyrolysis furnace along the flow path of the flue gas, wherein the third tube bank transfers heat between the flue gas and the hydrocarbon material;(V) flowing the hydrocarbon material from the convection section to the radiant section of the pyrolysis furnace to steam crack the hydrocarbon stream to generate a stream cracked effluent; and(VI) sequentially contacting the flue gas with the second tube bank, the third tube bank, and the first tube bank along the flow path of the flue gas.

2. The process of claim 1, wherein the convection section has a section length along the flow path of the flue gas, and the second tube bank is disposed in the upstream half of section length in the flow path of the flue gas.

3. The process of claim 2, the second tube bank is disposed in the upstream 30% of the section length in the flow path of the flue gas.

4. The process of any of claims 1 to 3, wherein the flue gas, upon entering the convection section, first contacts the second tube bank.

5. The process of any of claims 1 to 3, further comprising:(IV.5) flowing the hydrocarbon material exiting the third tube bank through a fourth tube bank disposed in the convection section of the pyrolysis furnace along the flow path of the flue gas, wherein the fourth tube bank transfers heat between the flue gas and the hydrocarbon material,and the fourth tube bank is disposed upstream of the third tube bank in the flow path of the flue gas.

6. The process of claim 5, wherein the fourth tube bank is disposed upstream of the second tube bank in the flow path of the flue gas.

7. The process of any of claims 1 to 4, wherein in step (IV), only a vapor is supplied into the third tube bank.

8. The process of any of claims 1 to 5, wherein step (III) further comprises depositing a first quantity of non-volatile material on the internal surface of the second tube bank.

9. The process of claim 8, wherein step (IV) further comprises depositing a second quantity of non-volatile material on the internal surface of the third tube bank, wherein the second quantity is no more than 20% of the first quantity.

10. The process of any of claims 1 to 9, further comprising:(VII) during a decoking interval, removing at least a portion of the non-volatile material on the internal surface of the second tube bank.

11. The process of claim 10, wherein during the decoking interval, the third tube bank has a temperature lower than in step (IV).

12. The process of any of claims 1 to 11, wherein at least 0.1 wt% of the hydrocarbon material is derived from plastic, based on the total weight of the hydrocarbon material.

13. The process of claim 12, wherein at least 50 wt% of the hydrocarbon material is derived from plastic, based on the total weight of the hydrocarbon material.

14. The process of claim 13, wherein at least 90 wt% of the hydrocarbon material is derived from plastic, based on the total weight of the hydrocarbon material.

15. The process of any of claims 1 to 11, wherein at least 50 wt% of the hydrocarbon material is a pyoil.

16. The process of any of claims 1 to 15, wherein step (I) comprises heating, via the first tube bank, the hydrocarbon material to a temperature Tl, where Td - 60 °C < Tl < Td, where Td is the dewpoint of the mixture of the hydrocarbon material and the added water and / or steam after step (II), and step (II) is carried out after step (I) and before step (III).

17. The process of claim 16, wherein Td - 20 °C < Tl < Td.

18. The process of any of claims 1 to 17, wherein step (II) comprises:(Ila) preheating the water and / or steam in a steam preheating tube bank in the convection section to obtain a preheated water and / or steam; and(lib) adding the preheated water and / or stream obtained in step (Ila) into the hydrocarbon material.

19. The process of any of claims 1 to 18, wherein step (II) occurs prior to step (III).

20. The process of any of claims 10 to 19, wherein online de-coking is carried out in step (VII).

21. A system, comprising: a pyrolysis furnace comprising a convection section and a radiant section, the convection section having a section length along a flow path of a flue gas generated in a radiant section of the pyrolysis furnace; a first tube bank, a second tube bank, and a third tube tank located in the convection section, each configured to flow a hydrocarbon material therethrough and to transfer heat between the flue gas and the hydrocarbon material; and an inlet for receiving water and / or steam into the hydrocarbon material, wherein: the first tube bank is upstream of the second tube bank, and the second tube bank is upstream of the third tube bank, in the flow path of the hydrocarbon material flowing therethrough; and the second tube bank is disposed upstream of the third tube bank along the flow path of the flue gas; andthe third tube bank is disposed upstream of the first tube bank along the flow path of the flue gas.

22. The system of claim 21, wherein the second tube bank is disposed in the upstream half of the section length in the flow path of the flue gas.

23. The system of claim 21 or claim 22, wherein the second tube bank is disposed in the upstream 30% of the section length in the flow path of the flue gas.

24. The system of any of claims 21 to 23, wherein the inlet is configured to direct the water and / or stream to the hydrocarbon material upstream of the second tube bank.

25. The system of any of claims 21 to 24, comprising a fourth tube bank configured to flow the hydrocarbon material therethrough, wherein the fourth tube bank is configured to transfer heat between the flue gas and the hydrocarbon material; and wherein the convection section is configured to flow the hydrocarbon material through the fourth tube bank after the third tube bank.

26. The system of claim 25, wherein the fourth tube bank is disposed upstream of the second tube bank along the flow of the flue gas.

27. The system of claim 25, wherein the second tube bank, the third tube bank, or both, are configured to flow the hydrocarbon material therethrough co-currently with the flow path of the flue gas.

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