EP4588992A1

EP4588992A1 - Method and system for steam cracking

Info

Publication number: EP4588992A1
Application number: EP24020026.1A
Authority: EP
Inventors: Tobias SINN; Christopher Eberstein
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2024-01-18
Filing date: 2024-01-18
Publication date: 2025-07-23
Also published as: WO2025153708A1

Abstract

There is provided a method of steam cracking one or more hydrocarbons, the method comprising preheating a liquid hydrocarbon feed stream (1) containing the one or more hydrocarbons to provide a preheated hydrocarbon feed stream (2), superheating a dilution steam stream (3) to provide superheated dilution steam stream (4), combining the preheated hydrocarbon feed stream (2) and the superheated dilution steam stream (4) to provide a gaseous steam cracking feed stream (6), and steam cracking the gaseus steam cracking feed stream (6) using a steam cracking arrangement (F) operated with electric energy, wherein at least 90% of of a heat amount used in said preheating the hydrocarbon stream (1) until its combination with the superheated dilution steam (4) is provided by transferring heat from steam to the hydrocarbon feed stream (1). A corresponding system (100, 200, 300, 400) for steam cracking is also provided.

Description

Technical Field

The present disclosure relates to methods and systems for electrically-powered steam cracking.

Background

Steam cracking of hydrocarbon feedstock is a common method for producing numerous desired petroleum-derived products. In many steam cracking processes, a hydrocarbon feedstock is supplied to a convection section of a steam cracking furnace. In the convection section, the hydrocarbon feedstock may be preheated to a higher intermediate temperature before being mixed with dilution steam and thereafter heated further to a temperature closer to a cracking temperature sufficient to carry out an endothermic reaction for cracking the hydrocarbons. The preheated hydrocarbon feedstock and dilution steam mixture may be fed to a radiation section of the steam cracking furnace, which may include radiant coils in which the mixture is further heated to a temperature sufficient for causing the endothermic reaction for cracking the hydrocarbons in the mixture. In gas-fired steam cracking furnaces, heat required for the convection section may be provided by hot effluent from the radiation section. The cracked mixture may thereafter be fed to a heat exchanger to rapidly quench the cracked mixture to minimize undesired post-cracking reactions and, in some instances, to recover heat from the process.
For further information regarding steam cracking technology, reference is made to expert literature, such as the article "Ethylene" in Ullmann's Encyclopedia of Industrial Chemistry, online publication 15 April 2009, DOI: 10.1002/14356007.a10_045.pub2, and to patent publications such as WO 2022/189422 A1 .
The heat for the radiation section may be provided by burning fuels containing hydrocarbons, such as natural gas. As mentioned in WO 2022/189422 A1 , however, ongoing efforts to reduce carbon dioxide emissions of industrial processes also extend to the operation of steam cracking furnaces. This may involve substituting conventional fuels by alternative fuels such as hydrogen, or by electrically-powered heating. Substantial modifications of the overall process may become necessary in this context, particularly in order to cope with the changed heat balance and reduced waste heat in comparison with conventional heating options.

Summary

According to the present disclosure, a method and an apparatus for steam cracking including the features of the independent claims is provided. Embodiments are the subject of the dependent claims and of the explanations below.
A method of steam cracking one or more hydrocarbons as proposed herein comprises preheating a liquid hydrocarbon feed stream containing the one or more hydrocarbons to provide a preheated hydrocarbon feed stream, superheating a dilution steam stream to provide superheated dilution steam stream, combining the preheated hydrocarbon feed stream and the superheated dilution steam stream to provide a gaseous steam cracking feed stream, and steam cracking the steam cracking feed stream using a steam cracking arrangement operated with electric energy. As proposed herein, at least 90% of a heat amount used in said preheating the feed stream until its combination with the superheated dilution steam is provided by transferring heat from steam to the hydrocarbon feed stream.
To avoid any misunderstandings, the "heat amount used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam" referred to herein is the amount of heat provided to the hydrocarbon feed stream such that this reaches a temperature at which it is combined with the dilution steam, i.e., there is particularly no further heating after the application of this heat amount and before the combination with the dilution steam. However, this particularly does, in some embodiments, not exclude that the hydrocarbon feed stream may be provided at an elevated temperature which does, however, typically not exceed 50 or 100 °C. Typically, the heat amount used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam does not generate substantial evaporation, i.e. the liquid hydrocarbon stream does typically not contain a vapor proportion of more than 10% when this is combined with the superheated dilution steam.
A "steam cracking arrangement operated with electric energy" includes at least one cracking furnace in which cracking coils are heated with electric energy, as further explained in more detail below. The term "furnace" is therefore used herein for non-fired, i.e., electrically operated, steam cracking apparatus as well.
The proposed method provides significant advantages for steam cracking systems with electrical furnaces where hot flue gas from firing as heat source to preheat, prevaporize and superheat the feed components such as hydrocarbons and dilution steam is not available. The present invention also provides advantages over solutions wherein feed preheating, prevaporization and superheating is performed using electricity. As, in the process as proposed therein, a major proportion or essentially all of the heat used for preheating the hydrocarbon feed stream is provided using steam as a heat medium, problems as described below can be avoided. This, and further aspects and advantages of the proposed method, will now be described in other words.
If provided by electrically-powered heating, hot flue gas effluent from the radiation section is not available for use by the convection section to evaporate and/or preheat the hydrocarbon feedstock. Thus, in such systems, heat for evaporation of the hydrocarbon feedstock and preheating of the hydrocarbon feedstock/dilution steam mixture may be provided by electrically-powered heaters. However, some hydrocarbon feedstocks contain mixtures of many hydrocarbon components resulting in the hydrocarbon feedstock having a wide boiling range. In addition, some hydrocarbon feedstocks may exhibit an elevated potential for fouling due to the presence of reactive molecules and contaminants, as well as amounts of high boiling material that may be more difficult to vaporize. As a result, heating some hydrocarbon feedstocks in order to provide a sufficient level of evaporation using electric heaters and/or a sufficient increase in temperature prior to being fed to a cracking furnace may result in an undesirably high amount of equipment fouling. Thus, for some hydrocarbon feedstocks, it may be difficult to sufficiently evaporate and/or preheat the hydrocarbon feedstock electrically without increasing the likelihood of causing fouling by one or more components of the hydrocarbon cracking mixture.
Electrical heating and vaporization of hydrocarbon feedstocks comes with extra challenges compared to that for conventional convection sections. In a convection section of a conventional feed-flue gas heat exchanger, the maximum tube metal temperature (TMT) can never be higher than the temperature of the flue gas. In comparison, electrical heaters operate with a constant heat flux and hence, the temperature at a specific spot of the heating element will depend strongly on the state of the liquid hydrocarbon feedstock. Surfaces of heating elements in contact with liquid have a much lower temperature than surfaces in contact with gas or gas bubbles. Consequently, bubble formation at the surface needs to be avoided, otherwise the heating element can foul leading to the failure of the electrical heater.
Embodiments of the method disclosed herein may be used for producing petroleum-derived products from hydrocarbon feedstocks that may be more accurately controlled or adjustable for different types of hydrocarbon feedstocks, and that are more efficient and/or more environmentally friendly. Embodiments described herein can be used for electrical steam cracking furnaces and for high efficiency fired furnaces with high degree of air preheating, which are processing heavy feedstocks having final boiling end points above ca. 350 °C in particular. Such feedstocks may, in certain embodiments, be heavy gasoils, hydrogenated vacuum gasoils (HVGO), hydrocracker residues (HCR) or heavy pyrolysis oils from plastic recycling, for example.
According to certain embodiments as provided herein, an amount of heat used for said superheating of dilution steam is at least in part provided by one or more electric heaters. The use of electric heaters may therefore, according to such embodiments, be restricted to steam heating or superheating where the fouling risks discussed herein are minimized. In certain embodiments, there is an "indirect" electric heating of the hydrocarbon feed by such steam which is in turn heated electrically.
According to certain embodiments as provided herein, the amount of heat used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam may be provided to the hydrocarbon stream in several steps, wherein a first part of said heat may be effective to provide an increase of the hydrocarbon feed stream temperature from a temperature level of 0 to 100 °C to a temperature level of 250 to 350 °C. A second part of said heat, may be effective to provide a further increase of the hydrocarbon feed stream to a temperature level of 400 to 450 °C. That is, in such embodiments, the "risky" temperature range is realized by steam heating which is either less prone to fouling or wherein fouling can be tolerated or coped in contrast to electric heating.
According to certain embodiments as provided herein, the amount of heat used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam may be provided using a first feed preheater and a second feed preheater, wherein the hydrocarbon feed stream or a part thereof is passed through the first feed preheater and then through the second feed preheater. This allows for utilizing distinct heating streams in these heat exchangers and to utilize the same or different steam types.
According to certain embodiments as provided herein, the first feed preheater is operated with steam at a pressure level of 60 to 130 bar absolute pressure and a temperature level not more than 50 K above the saturation temperature as a heating medium and the second feed preheater is operated with steam at a pressure level of 60 to 130 bar absolute pressure and a temperature level of 60 °C to 350 K above the saturation temperature as a heating medium. This is particularly the case when such steam is (non-process-)steam from a steam drum which is generated from heat transferred from a reactor effluent and which may be superheated in an electrically operated steam superheater. According to certain embodiments, steam for the first steam preheater may also be supplied from a different source, such as from a steam system, e.g. as an extraction stream from a steam turbine at elevated pressure.
According to other embodiments as provided herein, the first and the second feed preheater is operated with steam at a pressure level of 5 to 15 bar absolute pressure and a temperature level of 300 to 500 K above the saturation temperature as a heating medium. This is particularly the case when such steam is process or dilution steam which is later combined with the feed. This allows for exporting non-process steam from a steam drum which is generated from heat transferred from a reactor effluent.
In the latter embodiment, the steam with which the first and the second feed preheater is operated with may be electrically reheated or superheated at any position appropriate, particularly upstream and/or downstream of the first and/or the second feed preheater, in order to provide the necessary heat for the feed preheating and an appropriate temperature for combination with the feed.
Using different steam temperatures and pressures in the first and second feed preheaters allow for configurations wherein one of the feed preheaters can be configured to withstand high pressure steam levels, but at only moderate temperature levels, and the other can be configured to withstand higher temperature levels, but far lower steam pressure levels.
According to the embodiments just described, as mentioned, the steam used in the first feed preheater as the heating medium may be, or include, steam provided by a steam system in which heat from a cracked gas stream produced by the steamcracking is used for generating steam, and the steam used in the second feed preheater as the heating medium may be, or include, the dilution steam stream which is electrically superheated. This allows to put high temperature heat extracted from the cracked gas stream, e.g., in a transfer line exchanger, to an advantageous use, e.g. to minimize the electrical power demand of the feed preheating route.
Alternatively, the steam used in the first feed preheater as the heating medium and the steam used in the second feed preheater as the heating medium may be, or include, electrically superheated steam provided by a steam system utilizing heat from a cracked gas stream produced in the steamcracking of the steam cracking feed stream. As this steam is additionally electrically superheated, it can match the heating demands in the second feed preheater.
The steam used in the first feed preheater as the heating medium and the steam used in the second feed preheater as the heating medium may first be passed through the second feed preheater for transfer of sensible heat, and then through the first feed preheater for transfer of latent heat by steam condensation. This allows residual heat of the steam to be used downstream (in a perspective of the steam flow) of the second feed preheater in the first feed preheater, in order to extract a maximum amount of heat.
In a yet further alternative, the steam used in the first feed preheater as the heating medium and the steam used in the second feed preheater as the heating medium may be, or include, the dilution steam stream which is electrically superheated. In such a configuration, high pressure or very high pressure steam which may be produced using high temperature cracked gas heat may be exported or used for other tasks in the context of the proposed method.
In the alternative just described, the steam used in the first feed preheater as the heating medium and the steam used in the second feed preheater as the heating medium may first be passed through the first feed preheater and then through the second feed preheater, while transferring only sensible heat in each heat exchanger. Furthermore, it avoids the first and second feed preheaters to be designed for very high pressure steam levels.
According to certain embodiments as provided herein, the dilution steam and/or the steam cracking feed stream may be electrically superheated at any places where required, eliminating the need for direct electrical heating of the feed.
According to certain embodiments as provided herein, the one or more hydrocarbons may be provided as one or more constituents of at least one of a heavy gasoil, a hydrogenated vacuum gasoil, a hydrocracker residues and a heavy pyrolysis oils from plastic recycling. As the proposed embodiments avoid direct electric heating of such hydrocarbons, the proposed method is particularly advantageous for such "heavy" feeds. More generally, the proposed embodiments may be used with hydrocarbons having a final boiling point from 350 to 600 °C and/or a mean boiling point of 200 to 460 °C.
The system for steam cracking one or more hydrocarbons proposed herein is configured for preheating a liquid hydrocarbon feed stream containing the one or more hydrocarbons to provide a preheated hydrocarbon feed stream, superheating a dilution steam stream to provide superheated dilution steam stream, combining the preheated hydrocarbon feed stream and the superheated dilution steam stream to provide a gaseous steam cracking feed stream, and steam cracking the steam cracking feed stream using a steam cracking arrangement operated with electric energy. The proposed system is configured to provide at least 90% of of a heat amount used in said preheating the hydrocarbon stream until its combination with the superheated dilution steam by transferring heat from steam to the hydrocarbon feed stream.
As to the features and specific advantages of the proposed system, which preferably is adapted to perform a method as described hereinbefore and embodiments thereof, reference is made to the explanations above. Preferably, this arrangement comprises means adapted to perform any steps of a method as described.
Embodiments of the method disclosed herein may be used for preheating and evaporating hydrocarbon feedstocks without causing undesirably high fouling of electrical heaters; evaporating hydrocarbon feedstocks without causing failure of heating elements due to non-optimized evaporation behavior; and evaporating hydrocarbon feedstocks containing multiple hydrocarbons and/or having a wide boiling range. The present disclosure may address one or more of the above-referenced issues, as well as other possible issues.
Still other aspects and advantages of these exemplary embodiments and other embodiments, are discussed in detail herein. Moreover, it is to be understood that both the foregoing information and the following detailed description provide merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Accordingly, these and other objects, along with advantages and features of the present disclosure, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations.

Brief Description of the Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the present disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure, and together with the detailed description, serve to explain principles of the embodiments discussed herein. No attempt is made to show structural details of this disclosure in more detail than can be necessary for a fundamental understanding of the embodiments discussed herein and the various ways in which they can be practiced. According to common practice, the various features of the drawings discussed below are not necessarily drawn to scale. Dimensions of various features and elements in the drawings can be expanded or reduced to more clearly illustrate embodiments of the disclosure.

Short Description of the Figures

FIG. 1 schematically illustrates an example steam cracking system according to embodiments of the disclosure.
FIG. 2 schematically illustrates an example steam cracking system according to embodiments of the disclosure.
FIG. 3 schematically illustrates an example steam cracking system according to embodiments of the disclosure.

Detailed Description

The drawings may use like numerals to indicate like parts throughout the several views, the following description is provided as an enabling teaching of exemplary embodiments, and those skilled in the relevant art will recognize that many changes may be made to the embodiments described. It also will be apparent that some of the desired benefits of the embodiments described can be obtained by selecting some of the features of the embodiments without utilizing other features. Accordingly, those skilled in the art will recognize that many modifications and adaptations to the embodiments described are possible and may even be desirable in certain circumstances. Thus, the following description is provided as illustrative of the principles of the embodiments and not in limitation thereof.
As used herein, the term "plurality" refers to two or more items or components. The terms "comprising," "including," "carrying," "having," "containing," and "involving," whether in the written description or the claims and the like, are open-ended terms, i.e., to mean "including, but not limited to," unless otherwise stated. Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Use of ordinary terms such as "first," "second," "third," and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish claim elements. The term "and/or" means, inclusively, both "and" (conjunctive) as well as "or" (disjunctively).
The terms "gas" or "gaseous" are used interchangeably with "vapor," and mean a substance or mixture of substances in the gaseous state as distinguished from the liquid or solid state. Likewise, the term "liquid" means a substance or mixture of substances in the liquid state as distinguished from the gas or solid state.
The term "substantially" means "consisting essentially of," and includes "consisting of" generally and unless otherwise specified. For example, a composition that is "substantially free" of a specified compound or material may be free of that compound or material, or may have a minor amount of that compound or material present, such as through unintended contamination or incomplete purification. A "minor amount" may be a trace, an unmeasurable amount, an amount that does not interfere with a value or property, or some other amount as provided in context. A composition that has "substantially only" a provided list of components may consist of only those components, or have a trace amount of some other component present, or have one or more additional components that do not materially affect the properties of the composition.
Additionally, "substantially" modifying, for example, the type or quantity of an ingredient in a composition, a property, a measurable quantity, a method, a value, or a range, employed in describing the embodiments of the disclosure, refers to a variation that does not affect the overall recited composition, property, quantity, method, value, or range thereof in a manner that negates an intended composition, property, quantity, method, value, or range. For example, a substantially vaporized feed means that at least 80 wt.% or at least 85 wt.%, or at least 90 wt.%, or at least 95 wt.% or at least 99 wt.%, or at least 99.5 wt.%, or at least 99.9 wt.%, or at least 99.99 wt.%, of the feed is in a vapor phase, or all of the feed is an a vapor phase.
The term "heater" as used herein, in its broadest sense, refers to one or more devices that can be operated to collectively add heat to a stream and, unless otherwise stated, may include a combination of electrically powered heaters and heat exchangers using steam or other fluids (e.g., pyrolysis quench oil, pan oil, fuel oil product, kerosene, diesel, other gasoils, hydrotreated or hydrocracked gasoils, naphthalene, tar, coker oils, lube oils, residual un-vaporized components from the hydrocarbon feed stream, heat transfer fluids, silicone oils, ionic liquids, molten metals, flowable slurries, particulate mixtures, molten salts, commercially synthesized heat transfer fluids, and combinations thereof) as the high-temperature stream.
Different forms of steam are referred to herein, including saturated or superheated high pressure or very high pressure steam. Saturated high pressure steam may be steam at a temperature from 270 to 300 °C and a pressure from 60 to 80 bar. Superheated high pressure steam may be steam at a temperature from 350 to 450 °C and a pressure from 60 to 80 bar. Saturated very high pressure steam may be steam at a temperature from 300 to 350 °C and a pressure from 81 to 130 bar. Superheated very high pressure steam may be steam at a temperature from 450 to 550 °C and a pressure from 81 to 130 bar.
If reference is made to heat being provided by transferring heat from one stream to another stream, such as "from steam to the hydrocarbon feed stream," this is intended to refer to an indirect heat transfer, either via one or more heat transfer surfaces of a heat exchanger, or via a heat transfer fluid. It is particularly not intended to cover producing electrical energy from steam and later using the electrical energy for heating purposes. In contrast, an "electrical heater" uses electrical energy for heating purposes by means generally known in the art.
In conventional naphtha cracking, naphtha is vaporized and preheated in a convection section of a cracking furnace in a very specific way. First, the naphtha is substantially vaporized (typically, 85% or more of the naphtha is vaporized) in a bank of convection section tubes. Second, the substantially vaporized naphtha is mixed with superheated dilution steam, outside the convection section, to further vaporize the substantially vaporized naphtha. The substantially vaporized naphtha/steam mixture is then further heated in another bank of convection section tubes before being fed into the radiant section of the cracking furnace.
Vaporization in the first bank of convection section tubes occurs in a plug-flow manner. As the naphtha travels down the tube, a larger and larger fraction is vaporized.
Avoidance of crossing from a two-phase mixture to a fully vaporized mixture (or having a "dry point") in the convection section tubes is preferred because small amounts of heavies can deposit on the hot tube surface, which over time, can lead to significant fouling.
Low carbon emitting processes are ones where carbon dioxide emissions to the atmosphere are minimized or substantially eliminated. If we consider a low carbon emitting steam cracker that uses an electrically powered furnace, there will be no flue gas, hence no convection section, and, a new way to vaporize naphtha, as well as other hydrocarbon feedstocks, including, but not limited to, ethane, propane, C4-liquified petroleum gas, gas condensate, gas oil, diesel, jet fuel, gas-to-liquid fuel and bio feedstock, is required.
Electrically heated vaporizers are not conventional for multicomponent feedstocks. Electric heaters behave differently than conventional steam or flue gas fired heaters. They operate with constant heat flux across the heat generating element. Therefore, with two phases present (i.e., gas and liquid), where there are differences in thermal diffusivity among the phases (e.g., gas thermal diffusivity is less than liquid thermal diffusivity), inhomogeneous heat fluxes can lead to localized higher than desired heating element temperature which can lead to heating element burnout. Furthermore, and more specifically to steam cracking, having deposits of solid phase heavies on equipment near where full vaporization occurs is even more critically damaging to electric heaters since the resulting deposits will locally increase the thermal resistance leading to higher heating element temperatures generated on the resistive wire and heating element burnout. Commercial scale heating duty requirements for liquid feedstock vaporization service are greater than currently available electric heating technology in a single unit, so a number of heaters, placement, and controls also must be taken into account.
Designs to address the technical challenges for using electrically-powered heaters and furnaces are described herein.
There are a variety of specific flow schemes and options consistent with this broader concept and they are described in the figures and in the claims.
FIG. 1 schematically illustrates an example steam cracking system 100 according to embodiments of the disclosure.
The steam cracking system 100 includes a feed provision arrangement 110 and a steam cracking arrangement 120.
A liquid hydrocarbon feed stream 1 is provided to the feed provision arrangement 110 via a valve V1 which may be operated on the basis of a flow controller which is not shown for reasons of conciseness. This applies to other control units which may be part of steam cracking systems according to embodiments proposed herein. The hydrocarbon feed stream 1 is passed through a first feed preheater FPH-1 and then a second feed preheater FPH-2 to provide a preheated hydrocarbon feed stream 2.
A dilution steam stream 3 is also provided to the feed provision arrangement 110, a flow thereof being adjusted via valves V2 and V3, an operation of which may also be controlled by a flow control unit being the same as for valve V1 or different therefrom. Dilution steam stream 3 is initially passed through a first electrically operated dilution steam superheater DSSH-1 and thereafter through the second feed preheater FPH-2. Dilution steam stream 3 is thereafter passed through a second electrically operated dilution steam superheater DSSH-2, providing a superheated dilution steam stream 4.
Via valve V2, a part 4a of the superheated dilution steam stream 4 is passed to a first mixing unit M1 in which it is combined with the preheated hydrocarbon feed stream 2 for an at least partial evaporation thereof. A stream 5 withdrawn from first mixing unit M1 is passed to a second mixing unit M2 in which it is combined with a further part 4b of the superheated dilution steam stream 4 passed to the second mixing unit M2 via valve V2 to fully evaporate the feed. A steam cracking feed stream 6 thus formed from the hydrocarbon feed stream 1 and the dilution steam stream 3 in the feed provision arrangement 110 is passed to the steam cracking arrangement 120. Steam cracking feed stream 6 may, still in the feed provision arrangement 110 or in the steam cracking arrangement 120, be superheated in an electrically operated feed superheater FFSH operated on the basis of a temperature control unit, for example.
The steam cracking arrangement 120 comprises an electrically operated furnace box F in which the steam cracking feed stream 6 may be cracked in a manner as known per se from the prior art in one or more cracking furnaces. Any type of electrical heating may be applied in the furnace box F, and besides electrical energy, some amount of firing may also be applied.
A cracked gas 7 withdrawn from furnace box F may be quenched in a transfer line exchanger TLE or (primary) quench heat exchanger, which may be operated with water 8 from a steam drum S, generating steam 9 which is passed back to the steam drum S. Quenched cracked gas 10 is passed to further processing steps which are omitted in FIG. 1 for reasons of conciseness only. Boiler feed water 11 is supplied to steam drum D via a valve V4, for example on the basis of a level control unit.
From steam drum D, saturated very high pressure steam 12 may be withdrawn. A very high pressure steam superheater VHPSSH may optionally be provided, and superheated very high pressure steam 13 may be passed out of the system 100 via a valve V5 operated by a pressure control unit.
In system 100, a part 14 of the saturated very high pressure steam 12 is passed through the first feed preheater FPH-1 by restriction of a valve V6, where it is at least partly condensed. A stream 15 is passed to a condensate collector C in which a condensate 16 is collected which condensate 16 is pumped back to steam drum D using a high pressure condensate pump P.
To summarize what was said above, preheating of the liquid or heavy hydrocarbon feed stream 1 takes place in the two feed preheaters FPH-1 and FPH-2. The first stage preheating in first feed preheater FPH-1, is performed using condensing saturated very high pressure steam 14 from the steam drum D as a heat source. The second stage preheating in second feed preheater FPH-2 is performed using superheated dilution steam from the first electrical dilution steam superheater DSSH-1 as a heat source. The cooled dilution steam is again superheated in a second dilution steam superheater DSSH-2. The preheated heavy feed from FPH-2, which is still in liquid state, is partially prevaporized by injection of a first portion 4a of dilution steam in first mixing unit M1, which is superheated in the electrical dilution steam superheater DSSH-2. By adding the remaining portion of dilution steam 4b in second mixing unit M2, full evaporation is achieved. Before entering the furnace box F, the fully evaporated heavy feed/dilution steam mixture 6 is further superheated in the electrically operated final feed superheater FFSH.
The cracking reaction takes places in the furnace box F and the energy reguired is particularly or essentially provided by means of electrical heating. The electrical heating can be either direct (Joule) or indirect via radiation. As mentioned above, the term "furnace" and therefore the term "furnace box" as well are used herein for electrically powered steam cracking reactors as well, even if there is no firing by burners. Also reactor types such as the "Rotodynamic Reactor" or the "Rotating Olefins Cracker" known in the art may be used. The cracked gas leaving the e-furnace coil box is rapidly quenched in the quench exchangers including transfer line exchanger TLE to "freeze" the composition of the cracked gas 7 and to avoid undesired side reactions. The quench duty is used to generate saturated very high pressure steam 12 in the steam drum D, which is used as heat source for first stage feed preheating in first feed preheater. Excess very high pressure steam 12 is superheated in electrically operated very high pressure steam superheater VHPSSH.
In system 100, and in any further systems described herein in which a two-stage feed preheating is realized, hydrocarbon feed 1 may, in first feed preheater FPH-1 , be preheated to a temperature of, e.g., 250 to 350 °C, 275 to 325 °C, 290 to 310 °C, or ca. 300 °C using saturated, but essentially not, or only slighthly, superheated, very high pressure steam stream 14. For the second preheating step performed using second feed preheater FPH-2, in system 100, sensible heat of superheated process or dilution stream 3 at a temperature of, e.g, 550 to 600 °C, which is superheated in the first, electrically operated, dilution steam superheater DSSH-1 is used. This heating option for second feed preheater FPH-2 is also referred to as "option A" herein. Alternatively, as will now be shown in connection with FIG. 2, sensible heat of superheated very high pressure steam, which is superheated in electrically operated very high pressure steam superheater VHPSS upstream of the second feed preheater FPH-2 may be used. This alternative heating option is referred to as "option B" herein.
In both options A and B, and further embodiments proposed herein, direct electrical preheating of heavy feedstocks, which is not preferred due to fouling risks, is avoided. The instrumentalities proposed herein therefore establish an indirect electrical preheating of the liquid or heavy hydrocarbon feedstock 1. Also feedstock preheating by feed-effluent exchangers (FEX) having in this case high fouling risk is not necessary and avoided in embodiments as proposed herein.
FIG. 2 schematically illustrates an example steam cracking system 200 according to further embodiments of the disclosure. Elements which have already been described in connection with FIG. 1 and system 100 are indicated with like reference numerals.
As in system 100, a liquid hydrocarbon feed stream 1 is provided to the feed provision arrangement 110 via a valve V1. The hydrocarbon feed stream 1 is then passed, as above, successively through first feed preheater FPH-1 and second feed preheater FPH-2 to provide preheated hydrocarbon feed stream 2.
A dilution steam stream 3 is also provided to the feed provision arrangement 110, a flow thereof being adjusted via valves V2 and V3, as explained above. Dilution steam stream 3 is, different from system 100 according to FIG. 1, not passed through the first feed preheater FPH-1 or the second feed preheater FPH-2. Dilution steam stream 3 is passed through a single electrically operated dilution steam superheater DSSH, providing a superheated dilution steam stream 4.
In system 200, a part 14 of the superheated very high pressure steam 13 is passed through the second feed preheater FPH-2 and thereafter through the first feed preheater FPH-1 under restriction of valve V6, where it is at least partly condensed. As above, stream 15 is passed to a condensate collector C from which condensate 16 is pumped back to steam drum D using a high pressure condensate pump P.
Forming steam cracking feed stream 6 using the first mixing unit M1 and the second mixing unit M2 as well as operation of the steam cracking arrangement 120 has been described before in connection with system 100.
Again, aspects of system 200 will now be explained in other words. The preheating of the liquid or heavy feed stream 1 takes place in the two feed preheaters FPH-1 and FPH-2. In the first stage preheating in first feed preheater FPH-1 , the heat source is condensing saturated or only slightly superheated very high pressure steam coming from the second stage feed preheating in second feed preheater FPH-2. In the second stage preheating in second feed preheater FPH-2, the heat source is superheated very high pressure steam from the electrical very high pressure steam superheater VHPSSH. The preheated feed stream 2 from second feed preheater FPH-2, which is still in liquid state, is partially prevaporized by injection of a first portion 4a of dilution steam from the electrical dilution steam superheater DSSH in first mixing unit M. By adding the remaining portion 4b of dilution steam 4, which is superheated in the electrical dilution steam superheater DSSH, in second mixing unit full evaporation is achieved as already explained above.
Before entering furnace box F, the fully evaporated heavy feed/dilution steam mixture 6 is further superheated in the electrically final feed superheater FFSH. The cracking reaction takes places in the furnace box F and the energy required is provided by means of electrical heating. The electrical heating can be either direct (Joule) or indirect via radiation. The cracked gas 7 leaving the furnace box is rapidly quenched in the quench exchangers including transfer line exchanger TLE to "freeze" the composition and to avoid undesired side reactions. The quench duty is used to generate saturated very high pressure steam 12 in the steam drum D, which is used as heat source for first stage heavy feed preheating in first feed preheater FPH-1. Excess very high pressure steam is superheated in an electrically operated very high pressure steam superheater VHPSSH.
With the preheating scheme as shown for system 200, again basically an indirect electrical feed preheating is established. The risk of intense fouling, which would exist in case of direct electrical heating for feed vaporization, is avoided.
In general, both options A and B shown in FIG. 1 and 2 for system 100 and 200 are possible solutions for heavy feed processing in electrical cracking furnaces. Option A may be a preferred solution under certain circumstances, but option B may be an advantageous alternative if there are limitations in the available pressure drop of the dilution steam path for any reasons (e.g. in a revamp case) that does not allow going with option A. In another scenario, option B can be the concept of choice if a very high pressure steam superheater VHPSSH is required anyway for, e.g., steam conditioning for use in turbines allowing to minimize the equipment count in the dilution steam 2 superheating path. Furthermore, with both options of the invention,a wide feedstock flexibility ranging from light (gas, naphtha) to heavy feedstocks can be established for electrical cracking furnaces. In case of light feedstock operation, single or multiple heat exchangers might be dispensed of or by-passed.
To again summarize the advantages achievable according to the present disclosure, preheating/pre-vaporization of heavy or liquid feedstock 1 above temperatures of 290 to 310 °C is realized without involvement of direct electrical heating, which is prone to fouling and consequently prone to overheating and failure. Said feed preheating/prevaporization is realized by indirect electrical heating supplying the heat input to the feed stream via process steam 2 or very high pressure steam, which is electrically heated.
The methods proposed herein may be realized using known and referenceable heat exchanger types. The application of a feed-effluent exchanger, which directly or indirectly supplies heat to the feed stream, is not required. In case of heavy feedstocks and the intense fouling tendency of heavy feedstock cracked gases, the application of feed-effluent exchangers is limited due to the high performance loss over furnace runlength. Further more,other heat carrier media than those typically present in the furnace box F, which could be e.g. thermooils, are avoided.
Also combinations of options A and B referred to above in connection with systems 100 and 200 shown in FIG. 1 and 2 are contemplated herein. As shown in FIG. 3, an exclusively indirect electrical feed preheating train, which avoids the first and second feed preheaters FPH-1 and FPH-2 to be designed for very high pressure steam level can be realized.
FIG. 3 schematically illustrates an example steam cracking system 300 according to further embodiments of the disclosure. Elements which have already been described in connection with FIG. 1 and 2, i.e., systems 100 and 200, are again indicated with like reference numerals and repeated explanations are omitted.
In system 300, heating of the liquid hydrocarbon feed stream 1 is entirely realized by heat transfer from dilution steam stream 3. To this end, liquid hydrocarbon feed stream 1 is passed through first feed preheater FPH-1 and second feed preheater FPH-2. Dilution steam stream 3 is, in system 300, electrically heated in first dilution steam superheater DSSH-1, then passed through first feed preheater FPH-1, then electrically heated in second dilution steam superheater DSSH-2, then electrically heated in second dilution steam superheater DSSH-2, then passed through second feed preheater FPH-2, and then electrically heated in a third dilution steam superheater DSSH-2, providing superheated dilution steam stream 4.
Further aspects of steam cracking system 300 have already been described in connection with system 100 and 200.
In case of system 300, very high pressure steam export may be maximized. Also the high pressure condensate return to the steam drum D via the condensate drum C and a very high pressure pump P may be obsolete.
In summary, the feed provision arrangement 110 in the embodiments described before is configured to provide a steam cracking feed 6 to a furnace box F comprising one or more electrically-powered furnaces, to produce petroleum-derived products, such as, for example, olefins. The hydrocarbons contained in the hydrocarbon feed stream 1 may include, for example, multiple hydrocarbon components having much different boiling points, and in some embodiments, the hydrocarbon feed stream 1 may include, for example, one or more of ethane, propane, liquefied petroleum gas (e.g., C4-LPG), naphtha, gas condensate, gas oil, diesel, jet fuel, gas-to-liquid (GTL) fuel, pyrolysis oils, feedstocks derived from recycled plastics, or biofeedstock.
Embodiments as disclosed herein may be an advantageous option for high efficiency air preheated fired furnaces processing heavy feedstocks, for which the heat integration with feed-effluent exchangers is limited due to the high fouling tendency of the heavy feed cracked gas.
Having now described some illustrative embodiments of the disclosure, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the disclosure. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the disclosure are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments. It is, therefore, to be understood that the embodiments described herein are presented by way of example only and that, within the scope of any appended claims and equivalents thereto, the embodiments of the disclosure may be practiced other than as specifically described.
Furthermore, the scope of the present disclosure shall be construed to cover various modifications, combinations, additions, alterations, etc., above and to the above-described embodiments, which shall be considered to be within the scope of this disclosure. Accordingly, various features and characteristics as discussed herein may be selectively interchanged and applied to other illustrated and non-illustrated embodiment, and numerous variations, modifications, and additions further can be made thereto without departing from the scope of the present invention as defined in the appended claims.

Claims

A method of steam cracking one or more hydrocarbons, the method comprising preheating a liquid hydrocarbon feed stream (1) containing the one or more hydrocarbons to provide a preheated hydrocarbon feed stream (2), superheating a dilution steam stream (3) to provide superheated dilution steam stream (4), combining the preheated hydrocarbon feed stream (2) and the superheated dilution steam stream (4) to provide a gaseous steam cracking feed stream (6), and steam cracking the steam cracking feed stream (6) using a steam cracking arrangement (F) operated with electric energy, wherein at least 90% of of a heat amount used in said preheating the feed stream (1) until its combination with the superheated dilution steam (4) is provided by transferring heat from steam to the hydrocarbon feed stream (1).
The method according to claim 1, wherein an amount of heat used for said superheating of dilution steam or very high pressure steam is at least in part provided by one or more electric heaters (DSSH, DSSH-1, DSSH-2, VHPSSH).
The method according to claim 2, wherein the parts of the amount of heat used in said preheating the hydrocarbon stream (1) until its combination with the superheated dilution steam (4) is transferred to the hydrocarbon stream (1) in several steps.
The method according to claim 3, wherein a first part of the heat used in said preheating the hydrocarbon stream (1) until its combination with the superheated dilution steam (4) is effective to provide an increase of a temperature of the hydrocarbon feed stream (1) from a temperature level of 0 to 100 °C to a temperature level of 250 to 350 °C, and/or wherein a second part of the heat used in said preheating the hydrocarbon stream (1) until its combination with the superheated dilution steam (4) is effective to provide an increase of a temperature of the hydrocarbon feed stream (1) to a temperature level of 400 to 450 °C.
The method according to any one of claims 2 to 4, wherein the amount of heat used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam is provided using a first feed preheater (FPH-1) and a second feed preheater (FPH-2), and wherein the hydrocarbon feed stream (1) or a part thereof is passed through the first feed preheater (FPH-1) and then through the second feed preheater (FPH-2).
The method according to claim 5, wherein the first feed preheater (FPH-1) is operated with steam at a pressure level of 60 to 130 bar absolute pressure and a temperature level not more than 50 K above the saturation temperature as a heating medium and wherein the second feed preheater (FPH-2) is operated with steam at a pressure level of 60 to 130 bar absolute pressure and a temperature level of 60 °C to 350 °C above the saturation temperature as a heating medium.
The method according to claim 5, wherein the first feed preheater (FPH-1) and the second feed preheater (FPH-2) are operated with steam at a pressure level of 5 to 15 bar absolute pressure and a temperature level of 300 to 500 K above the saturation temperature as a heating medium.
The method according to claim 6, wherein the steam used in the first feed preheater (FPH-1) as the heating medium is or includes non-process steam, and wherein the steam used in the second feed preheater (FPH-2) as the heating medium is or includes the dilution steam stream (3) which is electrically superheated.
The method according to claim 8, wherein the non-process steam is provided by a steam system in which heat from a cracked gas stream (7) produced by the steamcracking is used for generating steam or by a further steam system.
The method according to claim 6, wherein the steam used in the first feed preheater (FPH-1) as the heating medium and the steam used in the second feed preheater (FPH-2) as the heating medium is or includes electrically superheated steam provided by a steam system utilizing heat from a cracked gas stream (7) produced in the steamcracking of the steam cracking feed stream (6).
The method according to claim 6, wherein the steam used in the first feed preheater (FPH-1) as the heating medium and the steam used in the second feed preheater (FPH-2) as the heating medium is first passed through the second feed preheater (FPH-2) and then through the first feed preheater (FPH-1).
The method according to claim 7, wherein the steam used in the first feed preheater (FPH-1) as the heating medium and the steam used in the second feed preheater (FPH-2) as the heating medium is or includes the dilution steam stream (3) which is electrically superheated.
The method according to claim 12, wherein the steam used in the first feed preheater (FPH-1) as the heating medium and the steam used in the second feed preheater (FPH-2) as the heating medium is first passed through the first feed preheater (FPH-1) and then through the second feed preheater (FPH-2) and/or is electrically reheated or superheated upstream and/or downstream of the the first feed preheater (FPH-1) and/or the second feed preheater (FPH-2).
The method according to any one of the preceding claims, wherein the one or more hydrocarbons are provided as one or more constituents of at least one of a heavy gasoil, a hydrogenated vacuum gasoil, a hydrocracker residues and a heavy pyrolysis oils from plastic recycling.
A system (100, 200, 300, 400) for steam cracking one or more hydrocarbons, the system (100, 200, 300, 400) being configured for preheating a liquid hydrocarbon feed stream (1) containing the one or more hydrocarbons to provide a preheated hydrocarbon feed stream (2), superheating a dilution steam stream (3) to provide superheated dilution steam stream (4), combining the preheated hydrocarbon feed stream (2) and the superheated dilution steam stream (4) to provide a gaseous steam cracking feed stream (6), and steam cracking the steam cracking feed stream (6) using a steam cracking arrangement (F) operated with electric energy, wherein the system (100, 200, 300, 400) is configured to provide at least 90% of of a heat amount used in said preheating the liquid hydrocarbon stream until its combination with the superheated dilution steam by transferring heat from steam to the hydrocarbon feed stream (1).