Systems & methods for recovering electrically generated thermal energy using molten salt in industrial processes

Abstract

This disclosure includes systems and methods for chemical production utilizing an electric furnace and a molten salt circuit to extract thermal energy from effluent exiting the furnace to preheat feedstock entering the furnace. Some such systems and methods utilize a feed preheat (FPH) heat exchanger through which feedstock passes before entering the furnace, and an effluent heat exchanger through which effluent passes after exiting the furnace, such that a molten salt can be circulated (1) through the effluent heat exchanger to extract thermal energy from the effluent and (2) through the FPH heat exchanger to transfer extracted thermal energy to the feedstock.

Description

SYSTEMS & METHODS FOR RECOVERING ELECTRICALLY GENERATED THERMAL ENERGY USING MOLTEN SALT IN INDUSTRIAL PROCESSESFIELD OF DISCLOSURE

[0001] The present disclosure relates generally to recovery of thermal energy in industrial processes and, more particularly but not by way of limitation, to systems, methods, and processes (e.g., for producing chemicals) in which thermal energy is recovered utilizing molten salt.BACKGROUND

[0002] Fired heaters or combustion furnaces are utilized to burn or combust a dedicated fuel to provide heat for a variety of purposes. For example, in chemical plants a fired heater can be utilized for cracking furnaces for olefins, reforming for MeOH and NH3, heaters for dehydrogenation, and the like. To further illustrate, these furnaces may provide heat of reaction for chemical synthesis, energy to heat one or more process streams, energy to vaporize liquids (e.g., boil water), energy to do work via steam (e.g., drive a compressor or pump), or energy for other process operations throughout the chemical production plant. Such burning or combustion of fuels results in the production of flue gases that can be subsequently used to recover heat. However, the flue gas contains CO2, which can be harmful to the environment.

[0003] The desire to reduce greenhouse gas emissions has recently prompted various approaches to reduce the reliance on fired furnaces in chemical production. One such approach is to replace fired heating by electrical heating. For example, WO 2020 / 150244 presents the use of electrified furnaces in ethylene production, and illustrates how other heat integration aspects, such as steam generation and furnace feed preheating, are likely to be affected in plants using electrified furnaces, relative to plants using conventional fuel-fired furnaces. A particular challenge is to effectively use the heat contained in the product from the furnace to preheat the feed to this furnace. Another example, WO 2023 / 025737 presents a solution to this challenge by the use of specially designed feed-to-effluent heat exchangers. Such heat exchangers may limit design flexibility or have other drawbacks that render them not suitable for all applications. The present inventors recognized a need to devise other solutions to effectively and reliably transfer heat from the process effluent to the process feed of an electrically heated furnace.SUMMARY

[0004] Electric furnaces have been proposed to replace fired furnaces in high-temperature chemical production processes where the emission of carbon dioxide (CO2) is to be reduced or eliminated. Such furnaces may, for example, use carbon-free electricity, for example renewable electricity, for their source of energy. However, the use of electric furnaces may require a process to be redesigned, which can be complicated, expensive, and introduce risk into otherwise established process systems.

[0005] Conventional fired furnaces for chemical production typically utilize steam generation as a means to cool effluent from the furnace, for example in a transfer line exchanger or waste heat boiler, while using the heat contained in the furnace flue gas for other duties such as preheating process feed. The first heat exchanger to cool the hot furnace effluent may be referred to as a transfer line exchanger (TLE), regardless of its means of cooling. In electric furnaces, no flue gas is generated, so the process feed must be preheated by other means. From the viewpoint of energy efficiency, it will usually be desirable to use the heat contained in the furnace process effluent to provide such preheat.

[0006] The systems and methods of the present disclosure instead utilize molten salt as a heattransfer fluid in a TLE. For example, the use of molten salt as a heat transfer fluid within the TLE allows for the TLE to have a smaller size, a higher heat-transfer coefficient (e.g., U-value) for faster cooling of the effluent (which may result in higher yield) and greater design flexibility. For example, in at least some configurations of the present systems, the molten salt heat exchangers are shell and tube heat exchangers that are configured for the process stream to flow on the tube side (through the tubes) of the heat exchanger, and for the molten salt to flow on the shell side of the heat exchanger (through the shell outside of the tubes), such that any coke formation can be cleaned relatively easily (e.g., by hydrojetting the interior of the tubes of the heat exchanger). This represents an advantage over conventional feed / effluent heat exchangers (TLEs) in which process steam flows on the shell side such that coking in the shell is significantly more difficult to clean

[0007] Some configurations of the present systems comprise: an electric furnace, a feed preheat (FPH) heat exchanger, an effluent heat exchanger, and a molten salt circuit. In some such configurations, the electric furnace has a fluid inlet, a fluid outlet, and a plurality of reactor tubes extending through the furnace between the fluid inlet and fluid outlet. In some such configurations, the FPH heat exchanger comprising a feed inlet, a feed outlet, a salt inlet, and a salt outlet, the FPHheat exchanger configured such that when a fluid feed flows from the feed inlet to the feed outlet and a molten salt flows from the salt inlet to the salt outlet, the fluid feed is in thermal communication but not fluid communication with the molten salt, where the feed outlet of the FPH heat exchanger is in fluid communication with the fluid inlet of the furnace. In some such configurations, the effluent heat exchanger comprises an effluent inlet, an effluent outlet, a salt inlet, and a salt outlet, the effluent heat exchanger configured such that when an effluent feed flows from the effluent inlet to the effluent outlet and a molten salt flows from the salt inlet to the salt outlet, the effluent feed is in thermal communication but not fluid communication with the molten salt, where the effluent inlet of the effluent heat exchanger is in fluid communication with the fluid outlet of the furnace. In some such configurations, the molten salt circuit comprises: a first conduit extending from the salt outlet of the effluent heat exchanger to the salt inlet of the FPH heat exchanger; a second conduit extending from the salt outlet of the FPH heat exchanger to the salt inlet of the effluent heat exchanger; and a molten salt; where the molten salt circuit is configured to circulate the molten salt sequentially through the effluent heat exchanger to receive thermal energy from the effluent, the first conduit, the FPH heat exchanger to transfer thermal energy from the molten salt to the fluid feed to preheat the fluid feed before it enters the furnace, and the second conduit.

[0008] In some of the foregoing configurations of the present systems, the effluent heat exchanger is a first effluent heat exchanger, and the system further comprises: a second effluent heat exchanger comprising an effluent inlet, an effluent outlet, a heat transfer fluid (HTF) inlet, and an HTF outlet, the second effluent heat exchanger configured such that when an effluent feed flows from the effluent inlet to the effluent outlet and an HTF flows from the HTF inlet to the HTF outlet, the effluent feed is in thermal communication but not fluid communication with the HTF, where the effluent inlet of the second effluent heat exchanger is in fluid communication with the fluid outlet of the first effluent heat exchanger. In some such configurations, the FPH heat exchanger is a first FPH heat exchanger, and the system further comprises: a second feed preheat (FPH) heat exchanger comprising a feed inlet, a feed outlet, an HTF inlet, and an HTF outlet, the second FPH heat exchanger configured such that when a fluid feed flows from the feed inlet to the feed outlet and an HTF flows from the HTF inlet to the HTF outlet, the fluid feed is in thermal communication but not fluid communication with the HTF, where the feed outlet of the second FPH heat exchanger is in fluid communication with the feed inlet of the first FPH heat exchanger.Some such configurations further comprise: a secondary FPH circuit comprising: a first HTF conduit extending from the HTF outlet of the second effluent heat exchanger to the HTF inlet of the second FPH heat exchanger; a second HTF conduit extending from the HTF outlet of the second FPH heat exchanger to the HTF inlet of the second effluent heat exchanger; and a heat transfer fluid (HTF), optionally where the HTF comprises H2O or thermal oil; where the secondary FPH circuit is configured to circulate the HTF sequentially through the second effluent heat exchanger to receive thermal energy from the effluent, the first HTF conduit, the second FPH heat exchanger to transfer thermal energy from the HTF to the fluid feed to preheat the fluid feed before it enters the first FPH heat exchanger, and the second HTF conduit.

[0009] In some of the foregoing configurations of the present systems, the molten salt circuit further comprises: a pump configured to circulate the molten salt.

[0010] In some of the foregoing configurations of the present systems, the molten salt circuit further comprises: an accumulator vessel in fluid communication with the first and second conduits. In some such configurations, the accumulator vessel is disposed at a low point in the molten salt circuit.

[0011] In some of the foregoing configurations of the present systems, the molten salt circuit further comprises: a heater configured to heat the molten salt when the molten salt is in the accumulator vessel.

[0012] In some implementations of the present methods of steam cracking, the method comprises: directing a hydrocarbon-containing fluid feed through a feed preheat (FPH) heat exchanger; directing the hydrocarbon-containing fluid feed from the FPH heat exchanger into a fluid inlet of an electric furnace and through a plurality of coils to heat the fluid feed to a reaction temperature and begin a cracking reaction, the fluid feed comprising a hydrocarbon feedstock and steam; directing an effluent from a fluid outlet of the furnace to an effluent inlet of an effluent heat exchanger to reduce the temperature of the effluent (e.g., to a temperature below the reaction temperature) and slow or stop the cracking reaction, the effluent heat exchanger comprising a salt inlet and a salt outlet, and configured such that when the effluent feed flows from the effluent inlet to an effluent outlet and a molten salt flows from the salt inlet to the salt outlet, the effluent feed is in thermal communication but not fluid communication with the molten salt; directing a molten salt at an elevated temperature from the salt outlet of the effluent heat exchanger to a salt inlet of the FPH heat exchanger to transfer thermal energy from the molten salt to the fluid feed, the FPHheat exchanger configured such that when the fluid feed flows from the feed inlet to the feed outlet and a molten salt flows from the salt inlet to the salt outlet, the fluid feed is in thermal communication but not fluid communication with the molten salt; and directing the molten salt at a reduced temperature from the salt outlet of the FPH heat exchanger to the salt inlet of the effluent heat exchanger to absorb thermal energy from the effluent. In some such implementations, the method further comprises adding steam to the hydrocarbon-containing fluid feed before directing the hydrocarbon-containing fluid feed into the furnace (e.g., before directing the hydrocarbon- containing fluid feed into the FPH heat exchanger).

[0013] In some of the foregoing implementations of the present methods, the elevated temperature is greater than 500°C and the reduced temperature is less than 400°C.

[0014] In some of the foregoing implementations of the present methods, the effluent heat exchanger is a first effluent heat exchanger, and the method further comprises: directing the effluent feed from the effluent outlet of the first effluent heat exchanger to an effluent inlet of a second effluent heat exchanger to further reduce the temperature of the effluent feed, the second effluent heat exchanger comprising a heat transfer fluid (HTF) inlet, and an HTF outlet, and configured such that when the effluent feed flows from the effluent inlet to the effluent outlet and an HTF flows from the HTF inlet to the HTF outlet, the effluent feed is in thermal communication but not fluid communication with the HTF. In some such configurations, the FPH heat exchanger is a first FPH heat exchanger, and the method further comprises: directing the fluid feed through a second feed preheat (FPH) heat exchanger, prior to directing the fluid feed through the first FPH heat exchanger, the second FPH heat exchanger comprising an HTF inlet, and an HTF outlet, and configured such that when the fluid feed flows through the second FPH heat exchanger and an HTF flows from the HTF inlet to the HTF outlet, the fluid feed is in thermal communication but not fluid communication with the HTF; directing a HTF at an elevated temperature from the HTF outlet of the second effluent heat exchanger to the HTF inlet of the second FPH heat exchanger to transfer thermal energy from the HTF to the fluid feed; and directing the HTF at a reduced temperature from the HTF outlet of the second FPH heat exchanger to the HTF inlet of the second effluent heat exchanger to absorb thermal energy from the feed effluent. In some such configurations, the HTF comprises H2O or thermal oil.

[0015] In some of the foregoing implementations of the present methods, a heat capacity rate of the molten salt (Cs) is greater than a heat capacity rate of the fluid feed (CF), optionally where Cs is 150% or more of CF, further optionally where Cs is 200% or more of CF.

[0016] In some of the foregoing implementations of the present methods, a heat capacity rate of the molten salt (Cs) is greater than a heat capacity rate of the effluent feed (CF), optionally where Cs is 120% or more of CF, further optionally where Cs is 140% or more of CF.

[0017] The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any embodiment of the present apparatuses, kits, and methods, the term “substantially” may be substituted with “within [a percentage] of’ what is specified, where the percentage includes 0.1, 1, 5, and / or 10 percent.

[0018] The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, an apparatus or kit that “comprises,” “has,” “includes” or “contains” one or more elements possesses those one or more elements, but is not limited to possessing only those elements. Likewise, a method that “comprises,” “has,” “includes” or “contains” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps.

[0019] Further, an apparatus, device or system that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described.

[0020] Any embodiment of any of the present apparatuses and methods can consist of or consist essentially of - rather than comprise / include / contain / have - any of the described steps, elements, and / or features. Thus, in any of the claims, the term “consisting of’ or “consisting essentially of’ can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.

[0021] Details associated with the embodiments described above and others are presented below.

[0022] Some details associated with the aspects of the present disclosure are described above, and others are described below. Other implementations, advantages, and features of the present disclosure will become apparent after review of the entire application, including the Brief Description of the Drawings, Detailed Description, and the Claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure is not always labeled in every figure in which that structure appears. Identical labels or reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers. Dimensioned figures are drawn to scale (unless otherwise noted), meaning the sizes of the depicted elements are accurate relative to each other for at least the embodiment depicted in the figures.

[0024] FIG. 1 depicts a block flow diagram of a generalized steam cracking plant or process.

[0025] FIG. 2 depicts a schematic diagram of a prior art hydrocarbon steam cracking system.

[0026] FIG. 3 depicts a schematic diagram of an example of a convection section of a prior art hydrocarbon steam cracking furnace of the system of FIG. 2.

[0027] FIG. 4 depicts a schematic diagram of a first example of the present systems utilizing molten salt for a heat transfer fluid in a transfer line exchange (TLE).

[0028] FIG. 5 depicts a schematic diagram of the system of FIG. 4 showing certain characteristics modeled for a given implementation of the system.

[0029] FIG. 6 depicts a schematic diagram of a second example of the present systems utilizing molten salt for a heat transfer fluid in a primary TLE and a second heat transfer fluid for a secondary TLE-feed preheat circuit.

[0030] FIG. 7 depicts a schematic diagram of the system of FIG. 6 showing certain characteristics modeled for a given implementation of the system.

[0031] FIG. 8 depicts a schematic diagram of a molten salt circuit of certain configurations of the present systems.DETAILED DESCRIPTION

[0032] Referring now to the drawings, and more particularly to FIG. 1, shown there is a block flow diagram of an example of a generalized steam cracking plant or process, which includes one or more of the following process sections for converting a feed stream 5 into a desired olefin product stream 50: a feed pretreatment section 10, a pyrolysis reaction section 20, a primary fractionation and compression section 30, a product fractionation (separation) section 40, or a combination thereof. Such sections will be described briefly in the next few paragraphs, and in more detail hereinbelow.

[0033] Feed pretreatment section 10 can be configured to adjust the pressure of a feed 5, possibly remove undesirable components (e.g., carbon dioxide (CO2), mercury, water) from a feed, combine an incoming feed with a stored feed to minimize variations in the feed to the pyrolysis reaction section 20, and / or preheat the feed 5, to provide a pretreated feed stream 15.

[0034] Pyrolysis reaction section 20 can comprise at least one steam cracking furnace or ‘pyrolysis’ furnace configured to crack hydrocarbons in the presence of steam to produce a cracked gas stream and a transfer line exchanger (TLE) or other heat transfer device to quench (and optionally harvest heat from) the cracked gas stream to provide a cooled cracked stream 25. Conventionally, the furnaces of a steam cracking plant create a high temperature environment by the combustion of fuels such as methane, which produces carbon dioxide emissions from a conventional steam cracking plant / process. However, in the present embodiments, the furnace is instead an electrically heated furnace, for example, a furnace in which electric heating elements provide heat or thermal energy in a heating chamber to tubes through which the feed stream flows.

[0035] The primary fractionation and compression section 30 can be configured to provide further heat recovery from and quenching of the cooled cracked gas stream 25, remove one or more components (e.g., fuel oil, hydrogen sulfide, carbon dioxide, water, or a combination thereof) from the cracked gas stream 25, and / or compress the cracked gas stream 25, thus providing a compressed cracked gas stream 38.

[0036] The product fractionation or separation section 40 can be configured to fractionate the compressed cracked gas stream 38, selectively hydrogenate one or more streams produced during the fractionation, and provide one or more olefin (e.g., ethylene, propylene) product streams 50. The product fractionation or separation section 40 may also provide one or more byproduct streams 60, such as, without limitation, a Ci stream, a C2 saturate stream, a C3 saturate stream, a C4 saturatestream, an acetylene stream, a butadiene stream, a 1-butene stream, an isobutylene stream, an aromatics stream, a hydrogen stream, a pyrolysis gasoline stream, and / or a pyrolysis fuel oil stream, or streams comprising a combination of these components. Some of these streams may be recycled to one or more sections of the steam cracking plant. For example, without limitation, the C2, C3, and / or C4 saturates streams may be recycled to one or more of the pyrolysis furnaces of the pyrolysis reaction section 20, hydrogen may be purified (e.g., via a pressure swing adsorption unit (PSA) and a methanation reactor to remove CO) and recycled to a hydrogenation reactor (e.g., a C2, C3, acetylene, or di-olefin hydrogenator) and / or utilized as a fuel source (e.g., via fuel cell). The Ci stream may be diverted for use as a fuel or chemical feedstock (e.g., for the production of hydrogen therefrom).

[0037] Referring now to FIGs. 2-3, FIG. 2 shows a more-detailed example of a prior art steam cracking furnace system 100 (derived from Ullman, Encyclopedia of industrial chemistry, p. 470 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim). System 100 comprises a steam cracking furnace 104, having a radiant section 108, and a convection section 112. The radiant section has burners 116 for heating a fired tubular reactor 120 wherein the actual steam cracking of the hydrocarbon feedstock occurs. The flue gas 124 from the burners 116 flows past the fired tubular reactor 120 to provide the necessary energy for the endothermic steam cracking process within the tubular reactor 120. The flue gas 124 subsequently flows to the convection section 112 of the steam cracking furnace 104.

[0038] Hydrocarbon feedstock can be introduced in an inlet stream 128, which is led to convection banks 132 for preheating in the convection section 112 of the steam cracking furnace. The components and function of convection banks 132 are described in more detail below with reference FIG. 3.

[0039] Boiler feed water is introduced in stream 136 which is also heated in the convection banks 132 and transferred to a steam drum 140. Steam from the steam drum 140 is superheated in the convection banks 132 to form a stream of superheated high pressure (VHP) steam 144. VHP steam normally has an absolute pressure in a range of 5.0 to 16.0 MPa. Dilution steam 148 is then injected in the hydrocarbon stream for mixing and performing the steam cracking process in the fired tubular reactor 120.

[0040] The cracked hydrocarbon gas flows from the fired tubular reactor 120 to a transfer line heat exchanger 152, where it is cooled and discharged in stream 156 for further processing. Theheat from the cracked gas recovered in the transfer line heat exchanger 152 is transferred to the steam drum 140.

[0041] FIG. 3 shows an example of a convection section 112 of a steam cracking furnace. In this example, hot flue gas 124 enters the convection section 112 at a high temperature, where heat is recovered by preheating the feedstock in convection bank Lower Mix Preheater (LMP) and preheating boiler feed water in convection bank economizer (ECO) and superheating the steam generated by the transfer line heat exchanger 152 in the Upper Superheater (USH) and Lower Superheater (LSH) of the convection banks 132. Liquid (e.g., light) hydrocarbon feedstock (128) is preheated and vaporized in Feed Pre Heater (FPH), mixed with dilution steam 148 and further heated in the Upper Mix Preheater (UMP) and LMP, before the preheated mixed stream 160 enters the fired tubular reactor 120 in the radiant section 108 of the furnace 104. Additional heat is recovered by preheating boiler feed water (e.g., 136) in the Economizer (ECO) of the convection banks 132, and superheating steam from the steam drum 140 in the USH, after which some boiler feed water is added at 164 to quench the temperature of the steam, which is then further superheated in the LSH convection bank, where superheated very high pressure steam is produced.

[0042] As explained above, steam cracking furnace 104 delivers heat at both radiant section 108 (e.g., from burner 116) and convection section 112 (e.g., via flue gas 124). It is desirable to eliminate or reduce the CO2 emissions from furnaces and other fired heaters. A promising approach to do this is to replace fired heaters with electric heaters. Many means of providing electric heating to furnaces have been described and can be envisioned, including, without limitation, direct ohmic heating of reaction tubes within a furnace, radiative heating by means of heating elements placed within the furnace, inductive heating, and heating in electrically driven rotating equipment (e.g,, rotodynamic reactors). For the purposes of this disclosure, all such equipment shall be considered electrically heated furnaces. A common feature of such electric heaters is that since they do not burn a fuel to produce heat, they do not produce flue gas that can be used as a heat source in subsequent processes (e.g., in the convection section described above). To compensate for the lack of the convection section, it is often necessary for the process heating equipment and heat integration scheme to be redesigned or for additional components (e.g., electrical resistive heaters) to be utilized. Accordingly, there is a need to provide a different means of heating hydrocarbon feed gas to the cracking furnace to substitute for heating in the convectionsection. As described herein, this disclosure provides such different heating means that can be implemented in existing or newly built cracker plants.

[0043] Referring now to FIGs. 4 and 5, shown there is a first example 200 of the present systems utilizing molten salt for a heat transfer fluid in a transfer line exchanger (TLE). More particularly, FIG. 4 depicts a schematic diagram of system 200, and FIG. 5 depicts a second schematic diagram of system 200 showing certain characteristics modeled for the system utilizing commercial process modeling software.

[0044] In the depicted example, system 200 is configured as an electrical steam cracking system. As shown, system 200 comprises: an electric furnace 204, a feed preheat (FPH) heat exchanger 208, an electric feed preheater 228, an effluent heat exchanger 212 (e.g., a transfer line exchanger (TLE)), and a molten salt circuit 216. Electric furnace 204 has a fluid inlet (left side of furnace 204), a fluid outlet (right side of furnace 204), and a plurality of reactor tubes 220 extending through the furnace between the fluid inlet and fluid outlet. FPH heat exchanger 208 comprises a feed inlet (left side of FPH heat exchanger 208), a feed outlet (right side of FPH heat exchanger 208), a salt inlet (top of FPH heat exchanger 208), and a salt outlet (bottom of FPH heat exchanger 208). FPH heat exchanger 208 is configured such that when a fluid feed flows from the feed inlet to the feed outlet (left to right in the depicted orientation) and a molten salt flows from the salt inlet to the salt outlet (top to bottom in the depicted orientation), the fluid feed is in thermal communication, but not fluid communication, with the molten salt. This arrangement, in which heat passes from one fluid to another through a solid wall without direct contact between the two fluids, is commonly referred to as indirect contact heat exchange, and the equipment in which it is implemented is referred to as an indirect contact heat exchanger. In various implementations (e.g., for steam cracking), the feed can comprise a hydrocarbon feedstock, for example ethane, propane, butane, naphtha, gas condensate, pyrolysis oil, and combinations thereof.

[0045] Effluent heat exchanger 212 comprises an effluent inlet (left side of effluent heat exchanger 212), an effluent outlet (right side of effluent heat exchanger 212), a salt inlet (bottom of effluent heat exchanger 212), and a salt outlet (top of effluent heat exchanger 212). Effluent heat exchanger 212 is configured such that when an effluent feed flows from the effluent inlet to the effluent outlet (left to right in the depicted orientation) and a molten salt flows from the salt inlet to the salt outlet (bottom to top in the depicted orientation), the effluent feed is in thermal communication, but not fluid communication, with the molten salt.

[0046] The feed outlet of FPH heat exchanger 208 is in fluid communication with the fluid inlet of furnace 204; for example, in the depicted configuration, the feed outlet of the FPH heat exchanger is in fluid communication with the fluid inlet of the furnace via an intervening supplemental feed preheater 228 configured to provide additional preheating of the feed before the feed enters furnace 204. In this configuration, dilution steam is added to the hydrocarbon feedstock via line 232 such that the feedstock alone is heated in FPH heat exchanger 208 and the mixture of feedstock and dilution steam are further heated in supplemental feed preheater 228. The effluent inlet of effluent heat exchanger 212 is in fluid communication with the fluid outlet of furnace 204, such that effluent can flow from the furnace to effluent heat exchanger 212. As shown, molten salt (MS) circuit 216 comprises: a first conduit 236 extending from the salt outlet of effluent heat exchanger 212 to the salt inlet of FPH heat exchanger 208; a second conduit 240 extending from the salt outlet of FPH heat exchanger 208 to the salt inlet of effluent heat exchanger 212; and a molten salt disposed in MS circuit 216. MS circuit 216 is configured to circulate the molten salt sequentially through: (1) effluent heat exchanger 212 to receive thermal energy from the effluent, (2) first conduit 236, (3) FPH heat exchanger 208 to transfer thermal energy from the molten salt to the feed to preheat the feed before it enters furnace 204, and (4) second conduit 240.

[0047] In some implementations, the molten salt comprises one or more salts selected from the group of salts consisting of: sodium nitrate (NaNCh), potassium nitrate (KNO3), lithium fluoride (LiF), and beryllium fluoride (BeF?). For example, in some implementations, the molten salt can comprise: (1) a mixture of 60% by weight sodium nitrate and 40% by weight potassium nitrate, which can be utilized in its liquid form at molten salt temperatures of from 260°C to 550°C; or (2) a mixture (e.g., 2:1 molar mixture, Li2[BeF4]) of lithium fluoride (LiF) and beryllium fluoride (BeF?), which can be used in its liquid form at molten salt temperatures of from 500°C to 700°C. Any other salt combination that will fit the purpose of this application can also be utilized; for example, other salts and salt mixtures that cover a wider temperature range and / or higher temperature level may increase the flexibility of the application.

[0048] In the depicted configuration, system 200 also comprises a second effluent heat exchanger 244 comprising an effluent inlet (left side of second effluent heat exchanger 244), an effluent outlet (right side of second effluent heat exchanger 244), a heat transfer fluid (HTF) inlet (bottom of second effluent heat exchanger 244), and an HTF outlet (top of second effluent heat exchanger 244). Second effluent heat exchanger 244 is configured such that when an effluent feedflows from the effluent inlet to the effluent outlet (left to right in the depicted orientation) and an HTF flows from the HTF inlet to the HTF outlet (bottom to top in the depicted orientation), the effluent feed is in thermal communication, but not fluid communication, with the HTF.

[0049] As shown, the effluent inlet of second effluent heat exchanger 244 is in fluid communication with the fluid outlet of first effluent heat exchanger 212 such that effluent can flow from first effluent heat exchanger 212 to second effluent heat exchanger 244. In the depicted configuration, second effluent heat exchanger 244 is configured to transfer thermal energy from the effluent to H2O, which leaves second effluent heat exchanger in a state of higher specific enthalpy (i.e., higher vapor fraction and / or higher temperature) than the state in which it entered (e.g., as liquid water, a mixture of liquid water and steam, or substantially all steam). In this configuration, second effluent heat exchanger 244 functions and may be referred to as a secondary transfer line exchanger (STLE), and first effluent heat exchanger 212 functions and may be referred to as a primary transfer line exchanger (PTLE). In this configuration, system 200 further comprises a steam circuit 248 in which steam exiting second effluent heat exchanger 244 can be used to provide thermal energy to various subparts 248 of the system. For example, steam exiting second effluent heat exchanger 244 may be considered medium pressure steam (MPS). MPS uses may include, for example, process heaters, direct steam generation, pumps, and / or the like. As thermal energy is extracted from the steam, a portion of the steam may condense, and the H2O stream can be passed through a condensate system 252 to return substantially the entire H2O stream to liquid form (e.g., boiler feed water (BFW)).

[0050] In certain implementations of the present methods of steam cracking (e.g., utilizing system 200), the method comprises: directing a fluid feed through a feed preheat (FPH) heat exchanger (e.g., 208) and into a fluid inlet of an electric furnace (e.g., 204) and through a plurality of coils (e.g., 220) to heat the fluid feed to a reaction temperature and begin a cracking reaction, where the fluid feed comprises a hydrocarbon feedstock and steam when it enters the electric furnace. In some implementations, the present methods of steam cracking can comprise: directing an effluent feed from a fluid outlet of the furnace (e.g., 204) to an effluent inlet of an effluent heat exchanger (e.g., 212) to reduce the temperature of the effluent feed to below the reaction temperature and slow or stop the cracking reaction. In some implementations, the present methods of steam cracking comprise: directing a molten salt at an elevated temperature from the salt outlet of the effluent heat exchanger (e.g., 212) to a salt inlet of the FPH heat exchanger (e.g., 208) totransfer thermal energy from the molten salt to the fluid feed. In some implementations, the present methods of steam cracking comprise: directing the molten salt at a reduced temperature from the salt outlet of the FPH heat exchanger (e.g., 208) to the salt inlet of the effluent heat exchanger (e.g., 212) to absorb thermal energy from the feed effluent. The elevated temperature, for example, may be greater than 500°C; and / or the reduced temperature, for example, may be less than 400°C.

[0051] In at least some such implementations, the present methods are carried out such that the heat capacity rate of the circulating molten salt is at least as large as (e.g., greater than, for example, 150%, 200%, 220%, 240% or more than) the heat capacity rate of the feed passing through the FPH heat exchanger, and is at least as large as (e.g., greater than, for example, 90%, 115%, 140%, or more than) the heat capacity rate of the effluent passing through the TLE. For example, in the depicted implementation, (1) the heat capacity rate of the molten salt is about 240% of the heat capacity rate of the feed passing through FPH heat exchanger 208; and, after steam is added to the feed at 232 and the combined feed / steam passes through furnace 204, (2) the same heat capacity rate of the molten salt is about 140% of the effluent passing through TLE 212. As used in this disclosure, heat capacity rate refers to the quantity of heat a flowing fluid (e.g., molten salt) is able to absorb or release per unit temperature change per unit time, and may be expressed according to the following Equation (1):C = cPm where C is heat capacity rate in units of W K'1, m is the mass flow rate of the fluid in units of kg-s'1, and cPis the specific heat of the fluid in units of J-kg'^K'1. Maintaining the ratio of heat capacity rate of the molten salt at or above the heat capacity rate of the fluid flowing through the furnace helps ensure that the low temperature reached by the molten salt exiting the FPH heat exchanger (e.g., 208) stays above the melting point of the molten salt (to avoid the molten salt freezing and clogging the molten salt circuit), and that the high temperature reached by the molten salt exiting the effluent heat exchanger 212 stays below the boiling point or degradation temperature of the molten salt.

[0052] In some implementations, the present methods of steam cracking further comprise: directing the effluent feed from the effluent outlet of the first effluent heat exchanger (e.g., 212) to an effluent inlet of a second effluent heat exchanger (e.g., 244) to further reduce the temperature of the effluent feed.

[0053] One example of system 200 was modeled using commercial process modeling software, specifically for a steam cracking process with a mass flowrate of hydrocarbon feedstock of 283 tonnes per hour, a mass flowrate of dilution steam of 85 tonnes per hour, and a mass flowrate of molten salt (a mixture of 60% sodium nitrate and 40% potassium nitrate) of 1650 tonnes per hour. The duties in megawatts (MW) of various components and temperatures in degrees Celsius are shown in FIG. 4; and the temperatures (°C), pressures (bar), mass flow rates (tonne / hr) at various points in the system — as well as duties (MW) of various components of the system — are shown in FIG. 5.

[0054] Referring now to FIGs. 6 and 7; FIG. 6 depicts a schematic diagram of a second example 200a of the present systems utilizing molten salt for a heat transfer fluid in a primary TLE and a second heat transfer fluid for a secondary TLE-feed preheat circuit; and FIG. 7 depicts a second schematic diagram of system 200a showing certain characteristics modeled for the system utilizing commercial process modeling software. System 200a is substantially similar to system 200, with the primary exceptions that system 200a includes a second TLE-FPH circuit that utilizes a second FPH heat exchanger to preheat the feedstock instead of second electric preheater 228. With the omission of preheater 228, the depicted example of system 200a directs the preheated mixture of feed and steam directly (i.e., without intervening active component), for example via a conduit, from FPH heat exchanger 208 to furnace 204. Other configurations of system 200a may also include a second electric preheater 228 to provide additional thermal energy. Also different from system 200, system 200a comprises a second feed preheat (FPH) heat exchanger 256 having a feed inlet (left side of second FPH heat exchanger 256), a feed outlet (right side of second FPH heat exchanger 256), an HTF inlet (top of second FPH heat exchanger 256), and an HTF outlet (bottom of second FPH heat exchanger 256). As with FPH heat exchanger 208, second FPH heat exchanger 256 is configured such that when a fluid feed flows from the feed inlet to the feed outlet (left to right in the depicted orientation) and an HTF flows from the HTF inlet to the HTF outlet (top to bottom in the depicted orientation), the fluid feed is in thermal communication but not fluid communication with the HTF. In system 200a, dilution steam is added to the hydrocarbon feedstock via line 232a between second FPH heat exchanger 256 and first FPH heat exchanger 208, such that the feedstock alone is heated in second FPH heat exchanger 256, and the mixture of feedstock and dilution steam is heated in first FPH heat exchanger 208. As shown, the feed outlet of second FPH heat exchanger 256 is in fluid communication with the fluid inlet of first FPH heatexchanger 208 such that the mixture of feedstock and dilution steam flows from second FPH heat exchanger 256 to first FPH heat exchanger 208.

[0055] In the depicted configuration, system 200a comprises a secondary FPH circuit 260. As shown, secondary FPH circuit 260 comprises: a first HTF conduit 264 extending from the HTF outlet of second effluent heat exchanger 244 to the HTF inlet of second FPH heat exchanger 256; and a second HTF conduit 268 extending from the HTF outlet of second FPH heat exchanger 256 to the HTF inlet of second effluent heat exchanger 244; and a heat transfer fluid (HTF). The HTF can comprise, for example, oil, H2O, or any other HTF that permits the system to function as described. In system 200a, secondary FPH circuit 260 is configured to circulate the HTF sequentially through: (1) second effluent heat exchanger 244 to receive thermal energy from the effluent, (2) first HTF conduit 264, (3) second FPH heat exchanger 256 to transfer thermal energy from the HTF to the fluid feed to preheat the fluid feed before it enters first FPH heat exchanger 208, and (4) second HTF conduit 268. Some such implementations may also include a steam drum and / or other components.

[0056] In certain implementations of the present methods of steam cracking (e.g., utilizing system 200a), the method comprises: directing a fluid feed through a feed preheat (FPH) heat exchanger (e.g., 208) and into a fluid inlet of an electric furnace (e.g., 204) and through a plurality of coils (e.g., 220) to heat the fluid feed to a reaction temperature and begin a cracking reaction, where the fluid feed comprises a hydrocarbon feedstock and steam when it enters the electric furnace. In some implementations, the present methods of steam cracking can comprise: directing an effluent feed from a fluid outlet of the furnace (e.g., 204) to an effluent inlet of an effluent heat exchanger (e.g., 212) to reduce the temperature of the effluent feed to below the reaction temperature and slow or stop the cracking reaction. In some implementations, the present methods of steam cracking comprise: directing a molten salt at an elevated temperature from the salt outlet of the effluent heat exchanger (e.g., 212) to a salt inlet of the FPH heat exchanger (e.g., 208) to transfer thermal energy from the molten salt to the fluid feed. In some implementations, the present methods of steam cracking comprise: directing the molten salt at a reduced temperature from the salt outlet of the FPH heat exchanger (e.g., 208) to the salt inlet of the effluent heat exchanger (e.g., 212) to absorb thermal energy from the feed effluent. The elevated temperature, for example, may be greater than 500°C; and / or the reduced temperature, for example, may be less than 400°C. In at least some such implementations, the present methods are carried out such that the heatcapacity rate of the circulating molten salt is at least as large as (e.g., greater than, for example, 90%, 115%, 140%, or more than) the heat capacity rate of each of the feed / steam passing through the FPH heat exchanger, and the effluent passing through the TLE. In this configuration of FIGs. 6 and 7, steam is added to the feed at 232a before the feed enters FPH heat exchanger 208, such that the heat capacity rate of the feed / steam passing through FPH heat exchanger is relatively close to (about equal to) the effluent passing through TLE 212.

[0057] In some implementations, the present methods of steam cracking further comprise: directing the effluent feed from the effluent outlet of the first effluent heat exchanger (e.g., 212) to an effluent inlet of a second effluent heat exchanger (e.g., 244) to further reduce the temperature of the effluent feed. Some such implementations further comprise: directing a HTF at an elevated temperature from the HTF outlet of second effluent heat exchanger (e.g., 244) to the HTF inlet of a second FPH heat exchanger (e.g., 256) to transfer thermal energy from the HTF to the fluid feed; and directing the HTF at a reduced temperature from the HTF outlet of second FPH heat exchanger 256 to the HTF inlet of second effluent heat exchanger 244 to absorb thermal energy from the feed effluent.

[0058] One example of system 200a was modeled using commercial process modeling software, specifically for a steam cracking process with a mass flowrate of hydrocarbon feedstock of 283 tonnes per hour, a mass flowrate of dilution steam of 85 tonnes per hour, and a mass flowrate of molten salt (a mixture of 60% sodium nitrate and 40% potassium nitrate) of 1650 tonnes per hour. The duties in megawatts (MW) of various components and temperatures in degrees Celsius are shown in FIG. 6; and the temperatures (°C), pressures (bar), mass flow rates (tonne / hr) at various points in the system — as well as duties (MW) of various components of the system — are shown in FIG. 7. As indicated, for the modeled example, system 200a is configured to recapture (via effluent heat exchangers 212 and 244) a greater portion of the thermal energy added by furnace 204 than is system 200 (via effluent heat exchanger 212) and, as a result, the amount of electric heating required for feed preheating needed for system 200a (via electric furnace 204) may be reduced (e.g., up to entirely eliminated) relative to system 200 (via electric preheater 228 and electric furnace 204). Additionally, further residual heat can be extracted from effluent exiting second effluent heat exchanger 244, for example, to heat other streams and / or generate steam.

[0059] As mentioned above, managing the relative magnitudes of the heat capacity rates of the molten salt and the process fluid through each of the molten salt heat exchangers (e.g., exchangers208 and 212 of systems 200 and 200a) is an important factor in effective operation of the overall system. While the heat capacity rate of the molten salt (Cs) will be (nearly) the same in both the FPH and the TLE exchangers, the heat capacity rate of the process stream in these two exchangers (CCF in the FPH heat exchanger, and CEF in the TLE) may be quite different. One reason for this is that the mass flow rate of the process streams through the exchangers may be different, for example because dilution steam is in some cases added after the process stream passes through the FPH heat exchanger. Another reason is that the chemical conversion in the electric furnace and the difference in temperature level of the process stream gives rise to different heat capacities for the two streams. Even so, the system must be configured and operated to allow the molten salt circuit to operate suitably in both exchangers, which means that the inlet ratio of heat capacity rates (CS / CCF) and the outlet ratio of heat capacity rates (CS / CEF) must both be considered.

[0060] FIG. 8 depicts a schematic diagram of a molten salt circuit 216a of certain configurations of the present systems. For illustration purposes, FIG. 8 shows only those components of molten salt circuit 216a, but it should be appreciated that the configuration of molten salt circuit 216a can be used in certain implementations of any of the present systems. In the configuration shown, in addition to the components described above with reference to FIGs. 4 and 5, circuit 216a further comprises a pump 272 and a salt accumulator 276. Pump 272 is configured to circulate the molten salt — i.e., from FPH heat exchanger 208 to effluent heat exchanger 212 through conduit 240, and from effluent heat exchanger 212 to FPH heat exchanger 208 through conduit 236. Salt accumulator 276 comprises a vessel in fluid communication with first and second conduits 236, 240 (e.g., in direct fluid communication with conduit 240 as shown). In some configurations, salt accumulator 276 is disposed at a low point in molten salt circuit 216a such that the molten salt can collect in the accumulator in the event of loss of power or heat — i.e., to allow for gravity draining of molten salt to the accumulator prior to the salt solidifying. Similarly, circuit 216a in at least some configurations includes a safe trip interlock to enable draining of salt while in a molten state to further mitigate the risk of salt freeze in a way that may otherwise interfere with operation of and / or damage the circuit (216a). In the depicted configuration, circuit 216a also includes a heater 280 configured to heat the molten salt when the molten salt is in the accumulator vessel. Heater 280 may be particularly useful during startup and shut down of a system (e.g., 200, 200a) to melt the salt to enable circulation.* * *

[0061] Additional details about various components of steam cracking plants and processes can be found in International Patent Application Publication No. W02020 / 150244, which is incorporated by reference in its entirety.

[0062] The above specification and examples provide a complete description of the structure and use of exemplary embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the present devices are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, components may be combined as a unitary structure, and / or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

[0063] The claims are not intended to include, and should not be interpreted to include, means- plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

Claims

CLAIMS1. A system comprising: an electric furnace having a fluid inlet, a fluid outlet, and a plurality of reactor tubes extending through the furnace between the fluid inlet and fluid outlet; a feed preheat (FPH) heat exchanger comprising a feed inlet, a feed outlet, a salt inlet, and a salt outlet, the FPH heat exchanger configured such that when a fluid feed flows from the feed inlet to the feed outlet and a molten salt flows from the salt inlet to the salt outlet, the fluid feed is in thermal communication but not fluid communication with the molten salt, where the feed outlet of the FPH heat exchanger is in fluid communication with the fluid inlet of the furnace; an effluent heat exchanger comprising an effluent inlet, an effluent outlet, a salt inlet, and a salt outlet, the effluent heat exchanger configured such that when an effluent feed flows from the effluent inlet to the effluent outlet and a molten salt flows from the salt inlet to the salt outlet, the effluent feed is in thermal communication but not fluid communication with the molten salt, where the effluent inlet of the effluent heat exchanger is in fluid communication with the fluid outlet of the furnace; a molten salt circuit comprising: a first conduit extending from the salt outlet of the effluent heat exchanger to the salt inlet of the FPH heat exchanger; a second conduit extending from the salt outlet of the FPH heat exchanger to the salt inlet of the effluent heat exchanger; and a molten salt; where the molten salt circuit is configured to circulate the molten salt sequentially through the effluent heat exchanger to receive thermal energy from the effluent, the first conduit, the FPH heat exchanger to transfer thermal energy from the molten salt to the fluid feed to preheat the fluid feed before it enters the furnace, and the second conduit.

2. The system of claim 1, where the effluent heat exchanger is a first effluent heat exchanger, and the system further comprises: a second effluent heat exchanger comprising an effluent inlet, an effluent outlet, a heat transfer fluid (HTF) inlet, and an HTF outlet, the second effluent heat exchanger configured such that when an effluent feed flows from the effluent inlet to the effluent outlet and an HTF flows from the HTF inlet to the HTF outlet, the effluent feed is in thermal communication but not fluid communication with the HTF, where the effluent inlet of the second effluent heat exchanger is in fluid communication with the fluid outlet of the first effluent heat exchanger.

3. The system of claim 2, where the FPH heat exchanger is a first FPH heat exchanger, and the system further comprises: a second feed preheat (FPH) heat exchanger comprising a feed inlet, a feed outlet, an HTF inlet, and an HTF outlet, the second FPH heat exchanger configured such that when a fluid feed flows from the feed inlet to the feed outlet and an HTF flows from the HTF inlet to the HTF outlet, the fluid feed is in thermal communication but not fluid communication with the HTF, where the feed outlet of the second FPH heat exchanger is in fluid communication with the feed inlet of the first FPH heat exchanger.

4. The system of claim 3, further comprising: a secondary FPH circuit comprising: a first HTF conduit extending from the HTF outlet of the second effluent heat exchanger to the HTF inlet of the second FPH heat exchanger; a second HTF conduit extending from the HTF outlet of the second FPH heat exchanger to the HTF inlet of the second effluent heat exchanger; and a heat transfer fluid (HTF), optionally where the HTF comprises H2O or thermal oil; where the secondary FPH circuit is configured to circulate the HTF sequentially through the second effluent heat exchanger to receive thermal energy from the effluent, the first HTF conduit, the second FPH heat exchanger to transfer thermal energy from the HTF to the fluid feed to preheat the fluidfeed before it enters the first FPH heat exchanger, and the second HTF conduit.

5. The system of any of claims 1-4, where the molten salt circuit further comprises: a pump configured to circulate the molten salt.

6. The system of any of claims 1-5, where the molten salt circuit further comprises: an accumulator vessel in fluid communication with the first and second conduits.

7. The system of claim 6, where the accumulator vessel is disposed at a low point in the molten salt circuit.

8. The system of any of claims 1-7, where the molten salt circuit further comprises: a heater configured to heat the molten salt when the molten salt is in the accumulator vessel.

9. A method of steam cracking, the method comprising: directing a hydrocarbon-containing fluid feed through a feed preheat (FPH) heat exchanger; directing the hydrocarbon-containing fluid feed from the FPH heat exchanger into a fluid inlet of an electric furnace and through a plurality of coils to heat the fluid feed to a reaction temperature and begin a cracking reaction; directing an effluent from a fluid outlet of the furnace to an effluent inlet of an effluent heat exchanger to reduce the temperature of the effluent, the effluent heat exchanger comprising a salt inlet and a salt outlet, and configured such that when the effluent feed flows from the effluent inlet to an effluent outlet and a molten salt flows from the salt inlet to the salt outlet, the effluent feed is in thermal communication but not fluid communication with the molten salt; directing a molten salt at an elevated temperature from the salt outlet of the effluent heat exchanger to a salt inlet of the FPH heat exchanger to transfer thermal energy from the molten salt to the fluid feed, the FPH heat exchanger configured such that when the fluid feed flows from the feed inlet to the feed outlet and a moltensalt flows from the salt inlet to the salt outlet, the fluid feed is in thermal communication but not fluid communication with the molten salt; and directing the molten salt at a reduced temperature from the salt outlet of the FPH heat exchanger to the salt inlet of the effluent heat exchanger to absorb thermal energy from the effluent; where the method optionally further comprises adding steam to the hydrocarbon- containing fluid feed before directing the hydrocarbon-containing fluid feed into the furnace and, optionally before directing the hydrocarbon-containing fluid feed into the FPH heat exchanger.

10. The method of claim 9, where the elevated temperature is greater than 500°C and the reduced temperature is less than 400°C.

11. The method of any of claims 9-10, where the effluent heat exchanger is a first effluent heat exchanger, and the method further comprises: directing the effluent feed from the effluent outlet of the first effluent heat exchanger to an effluent inlet of a second effluent heat exchanger to further reduce the temperature of the effluent feed, the second effluent heat exchanger comprising a heat transfer fluid (HTF) inlet, and an HTF outlet, and configured such that when the effluent feed flows from the effluent inlet to the effluent outlet and an HTF flows from the HTF inlet to the HTF outlet, the effluent feed is in thermal communication but not fluid communication with the HTF.

12. The method of claim 11, where the FPH heat exchanger is a first FPH heat exchanger, and the method further comprises: directing the fluid feed through a second feed preheat (FPH) heat exchanger, prior to directing the fluid feed through the first FPH heat exchanger, the second FPH heat exchanger comprising an HTF inlet, and an HTF outlet, and configured such that when the fluid feed flows through the second FPH heat exchanger and an HTF flows from the HTF inlet to the HTF outlet, the fluid feed is in thermal communication but not fluid communication with the HTF;directing a HTF at an elevated temperature from the HTF outlet of the second effluent heat exchanger to the HTF inlet of the second FPH heat exchanger to transfer thermal energy from the HTF to the fluid feed; and directing the HTF at a reduced temperature from the HTF outlet of the second FPH heat exchanger to the HTF inlet of the second effluent heat exchanger to absorb thermal energy from the feed effluent.

13. The method of any of claims 11-12, where the HTF comprises H2O or thermal oil.

14. The method of any of claims 9-13, where a heat capacity rate of the molten salt (Cs) is greater than a heat capacity rate of the hydrocarbon-containing fluid feed (CF), optionally where Cs is 150% or more of CF, further optionally where Cs is 200% or more of CF.

15. The method of any of claims 9-14, where a heat capacity rate of the molten salt (Cs) is greater than a heat capacity rate of the effluent feed (CF), optionally where Cs is 120% or more of CF, further optionally where Cs is 140% or more of CF.

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