Systems & methods for storing thermal energy and electrically heating gas in chemical production

Abstract

This disclosure includes systems and methods of operating a convection section of an furnace in a chemical production process with simulated combustion gas (SCG) that is heated by an electric or thermal energy source instead of by combustion. Some such systems and methods utilize a thermal mass that is configured to store thermal energy such that the thermal mass can be used to heat a working fluid. The thermal mass can be coupled to a heater that receives electrical energy from a renewable source, and converts the electrical energy into thermal energy to heat the thermal mass and thereby store the thermal energy. In some aspects, a furnace is in fluid communication with the thermal mass such that the furnace receives the working fluid from the thermal mass to provide thermal energy to process for chemical production that would otherwise typically be provided by flue gas from a hydrocarbon-fired radiant section in conventional systems. In some configurations, the working fluid is or comprises one or more radiatively participating gases heated to exceed a threshold above which the working fluid transfers heat through radiation.

Description

SYSTEMS & METHODS FOR STORING THERMAL ENERGY AND ELECTRICALLY HEATING GAS IN CHEMICAL PRODUCTIONFIELD OF DISCLOSURE

[0001] The present disclosure relates generally to processes for producing and utilizing heated gas and, more particularly but not by way of limitation, to processes for producing and utilizing heated gas in low- or no-carbon chemical processes and systems powered by renewable energy.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 used as a diluent), energy to do work (e.g., drive a compressor or pump), or energy for other process operations throughout the chemical synthesis 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] Some efforts have been made to convert certain aspects of chemical synthesis plants to electrical power instead of convection. However, the electrification of certain components in chemical synthesis plants presents additional issues and challenges that are different than and / or not necessarily present in combustion-driven furnace reactors.SUMMARY

[0004] Electric heaters / fumaces have been proposed to replace fired heaters / furnaces in processes where the emission of carbon dioxide (CO2) is to be reduced or eliminated. However, the use of electric heaters / fumaces may require a process to be completely redesigned, which can be complicated, expensive, and introduce risk into otherwise established process systems. To illustrate, electric furnaces have no combustion production and, therefore, no flue gas. In processes that have conventionally utilized the heat from the flue gas (e.g., a convection section of a conventional furnace), this heat must now come from somewhere else. Electric furnaces arerelatively new to the chemical process industry and improved designs to overcome the lack of heat from flue gas are needed.

[0005] The systems and methods of the present disclosure provide a manner for overcoming certain deficiencies found in fired and electric furnaces. For example, the present systems, methods, and processes contemplate — in conjunction with the reduction or elimination of combustion in a radiation section of a furnace — the use of external sources of heated gas in lieu of combustion gases, with such gas at least partially heated by external electrical heating elements either directly (e.g., by the heating elements) or indirectly (e.g., by a thermal mass that is heated by the heating elements and stores thermal energy). Such heating elements may, for example, include electrical wires mounted to refractor bricks, conductive refractory bricks, or the like.

[0006] In some configurations of the present systems for heating a chemical process, the system comprises: a thermal mass configured to store thermal energy; a heater configured to heat the thermal mass; where the thermal mass is configured to heat a gaseous working fluid as the working fluid flows in thermal communication with the thermal mass; and a furnace comprising a convection section configured to receive the heated working fluid from the heater to transfer thermal energy from the working fluid to at least one heat exchanger disposed within the convection section.

[0007] In some of the foregoing configurations of the present sytsems, the furnace further comprises: a radiant section comprising a tubular reactor and one or more electric heating elements, the radiant section configured to receive the heated working fluid such that the tubular reactor is heated by a combination of thermal energy provided by the heating element(s) and thermal energy provided by the working fluid; where the convection section is configured to receive the heated working fluid through the radiant section.

[0008] In some of the foregoing configurations of the present systems, the working fluid comprises one or more radiatively active species, selected from a list of radiatively active species consisting of: carbon dioxide, methane, water vapour, ozone, and nitrous oxide.

[0009] In some of the foregoing configurations of the present systems, the working fluid is substantially free of N2 and Oxygen.

[0010] In some of the foregoing configurations of the present systems, the heater comprises a plurality of electric heating element. In some such configurations, the heating elements are in direct thermal communication with the thermal mass.

[0011] In some of the foregoing configurations of the present systems, the thermal mass defines a plurality of passages configured to receive working fluid such that the thermal mass is configured to contact and convectively heat the working fluid.

[0012] In some of the foregoing configurations of the present systems, the thermal mass comprises a plurality of conduits distinct from the thermal mass and configured to receive working fluid such that the thermal mass is configured to radiatively heat the conduits.

[0013] In some of the foregoing configurations of the present systems, the system further comprises: a process line in fluid communication with upstream and downstream sides of the thermal mass; a bypass line in communication with the process line upstream and downstream of the thermal mass such that the bypass line is configured direct a portion of the working fluid around the thermal mass; and a bypass valve that is actuatable to control the respective amounts of working fluid from the process line that are delivered to: the bypass line; and the thermal mass. Some such configurations further comprise: a processor in communication with the power source and the bypass valve, the processor configured to: based on a detection of a first event, actuate the power source to deliver electricity to the heater, wherein the first event is selected from the group of events consisting of: a price of electricity from a power grid being less than a non-peak threshold; and an amount of electricity from a renewable power supply being greater than a surplus threshold; or based on at least a temperature of the thermal mass, actuate the bypass valve such that a temperature of the working fluid entering the furnace is within a target temperature range.

[0014] In some implementations of the present methods of retrofitting a combustion furnace to be electrically heated, the method comprises: discontinuing, at a fired furnace having a radiant section and a convection section, operation of one or more gas burners configured to ignite a combustible gas within the radiant section; providing a thermal mass in a process line that is configured to deliver a gaseous working fluid to the radiant section and through a convection section of the furnace, the thermal mass coupled to a heater that is configured to receive electricity from a renewable power source to generate and store thermal energy; and conveying the working fluid through one or more gaps or passages of the thermal mass to heat the working fluid, and conveying the working fluid from the thermal mass to convection section of the furnace to heat at least one heat exchanger disposed within the convection section.

[0015] In some of the foregoing implementations of the present methods of retrifitting, the method further comprises: installing an electrically heated tubular reactor and configuring a process line to deliver a feedstock to the electrically heated tubular reactor.

[0016] In some of the foregoing implementations if the present methods of retrifitting, the method further comprises: installing one or more electric heating elements in the radiant section; and configuring the radiant section to receive the heated working fluid from the thermal mass such that the heated working fluid first adds thermal energy to a tubular reactor in the radiant section and is then conveyed to the convection section of the furnace.

[0017] In some implementations of the present processes for operating a convection section of a chemical production system without combustion of hydrocarbons in a radiant section of the system, the process comprises: heating a gaseous working fluid by conveying the working fluid through one or more gaps or passages defined in a body of a thermal mass that is coupled in thermal communication with a heater that is configured to heat the thermal mass; and conveying the heated working fluid from the thermal mass to the convection section to provide thermal energy to one or more heat exchangers disposed within the convection section.

[0018] In some of the foregoing implementations of the present processes for operating a convection section, conveying the working fluid to the convection section comprises: powering electrical heating elements in a radiant housing defining a radiant section to heat a tubular reactor within the radiant housing; where the working fluid is conveyed to the convection section via the radiant section such that the working fluid provides thermal energy to heat the tubular reactor before the working fluid reaches the radiant section.

[0019] In some of the foregoing implementations of the present processes for operating a convection section, the process further comprises: adjusting a bypass valve to convey working fluid through a bypass line that bypasses the thermal mass.

[0020] In some of the foregoing implementations of the present processes for operating a convection section, the working fluid comprises one or more radiatively active species, selected from a list of radiatively active species consisting of: carbon dioxide, methane, water vapour, ozone, and nitrous oxide.

[0021] 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. Theterm “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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Details associated with the embodiments described above and others are presented below.

[0026] 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

[0027] 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 inwhich 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.

[0028] FIG. 1 depicts a block flow diagram of a generalized steam cracking plant or process.

[0029] FIG. 2 depicts a schematic diagram of a prior art hydrocarbon steam cracking system.

[0030] 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.

[0031] FIG. 4A depicts a schematic diagram of an open-loop example of a portion of a chemical production system of the present disclosure.

[0032] FIG. 4B depicts a schematic diagram of a closed-loop example of a portion of a chemical production system of the present disclosure.

[0033] FIG. 5 depicts a schematic diagram of a further example of a chemical production system of the present disclosure.

[0034] FIG. 6A depicts a schematic diagram of a further example of a chemical production system of the present disclosure.

[0035] FIG. 6B depicts an enlarged view of the region 6B in FIG. 6A, which depicts an example of an electric radiant housing of the system of FIG. 6 A.

[0036] FIGs. 7A and 7B depict sectional front and sectional top views, respectively, of an example of a heater of the heat production systems of the present disclosure.

[0037] FIGs. 8A and 8B depict sectional front and top views, respectively, of another example of a heater of the heat production systems of the present disclosure.

[0038] FIG. 9A and 9B depict sectional front and top views, respectively, of another example of a heater of the heat production systems of the present disclosure.DETAILED DESCRIPTION

[0039] 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 primaryfractionation and compression section 30, a product fractionation (separation) and compression section 40, or a combination thereof. Such sections will be described briefly in the next few paragraphs, and in more detail hereinbelow.

[0040] 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.

[0041] Pyrolysis reaction section 20 can comprise at least one steam cracker 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 a radiative electric furnace in which electric heating elements provide heat or thermal energy in a heating chamber to tubes through which the feed stream flows.

[0042] 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.

[0043] 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 saturate stream, 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 thepyrolysis 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 also be recycled for use as a fuel (e.g., for the production of hydrogen therefrom).

[0044] 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.

[0045] Hydrocarbon feedstock can be introduced in an inlet stream 128, which is led to convection bank 132 for preheating in the convection section 112 of the steam cracking furnace. The components and function of convection bank 132 are described in more detail below with reference FIG. 3.

[0046] Boiler feed water is introduced in stream 136 which is also heated in the convection bank 132 and transferred to a steam drum 140. Steam from the steam drum 140 is superheated in the convection bank 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. Steam 148 is then injected in the hydrocarbon stream for mixing and performing the steam cracking process in the fired tubular reactor 120.

[0047] 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, i.e., distillation. The heat from the cracked gas recovered in the transfer line heat exchanger 152 is transferred to the steam drum 140.

[0048] 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) andpreheating 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 bank 132. Light hydrocarbon feedstock of naphtha (e.g., 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 bank 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.

[0049] 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). Recently, furnaces (e.g., 104) and other fired heaters are being replaced or eliminated to cut back on the production of CO2 emissions. Most commonly, the fired heaters are replaced with electric heaters. For example, heaters with radiating elements (e.g., Kanthal heater, Riken heater, etc.) may be utilized by applying a voltage across metal wires or ribbons to produce heat via ohmic or impedance heating. However, as these electric heaters do not burn or combust material to produce heat, they do not produce flue gas that can be used as a heat source in subsequent processes. To compensate for the lack of the convection section, it is often necessary for the process heat integration scheme to be redesigned or for additional components (e.g., multiple electrical resistive heaters) to be utilized. Accordingly, there is a need to provide a hot gas substitute for flue gas in systems and processes where fired heaters are replaced with alternative energy sources. As described herein, this disclosure provides hot gas substitutes for various processes that do not require significant alterations to existing processes or excessive cost and that do not sacrifice heat generation.

[0050] Referring now to FIGs. 4A-8B, some configurations of the present disclosure includes a system in which a heat storage device 210 can be used to heat a working fluid that is subsequently used to deliver heat (thermal energy) to a process or other apparatus (e.g., heat exchange reactor). Device 210 may be referred to herein as a heater given its primary function of heating a working fluid; however, that does not require heater 210 to actively convert electrical energy to thermal energy. For example, in some configurations, device or heater 210 can be configured to operate as a furnace or heater in which heat from the heater is continuously delivered to a working fluid toachieve a result such as in a chemical process, which can, for example, correspond to one of: a steam cracking process (e.g., an ethane (C2H6) cracking process or a steam cracking for olefins process, in some examples); a steam methane reforming (SMR) process (e.g., for syngas production); an ammonia, hydrogen, or methanol process; a dehydrogenation process (e.g., of propane to propylene); and a tar cracking process, or the like. By way of further example, in other configurations, device or heater 210 can comprise a thermal mass (e.g., refractory bricks) that is in thermal communication with one or more heating elements (e.g., electric heating elements, conductive refractory bricks, and / or other sources of thermal energy) to heat the thermal mass (e.g., directly, such as radiatively; and / or indirectly, via a working fluid flowing heated by the heating elements and then flowing in thermal communication with the thermal mass) and thereby store thermal energy. Such heating elements may, for example, be configured to convert electrical energy into thermal energy.

[0051] For example, FIGs. 4A and 4B depict open- and closed-loop configurations, respectively, of a system 200 in which heater 210 is configured to provide thermal energy to one or more heat exchangers 226 disposed within a convection housing 230 (e.g., into a channel defined by the convection section), for example, of a cracking reactor system (which would typically receive combustion flue gas from a radiant section). Convection housing 230 can be similar to that of a convection section in a traditional fired heater so that an existing furnace may be retrofitted to be utilized in system 200. As an illustrative example, an existing furnace can be modified so that working fluid is ducted to existing banks in the convection section, and process and structural reconfigurations can be kept to a minimum. Heat exchangers 226 may be associated with various process and utility streams as is known in the art.

[0052] In the depicted configurations, system 200 includes a process line 234 that is configured to circulate a working fluid through heater 210 and convection housing 230, and a bypass line 238 that is configured to provide a path for some or all of the working fluid to bypass the heater. As shown, process line 234 can include a first section 242 coupled to inlet of heater 210 and deliver the working fluid to the heater, a second section 246 coupled to outlet of the heater and convey the working fluid from the heater to convection housing 230, and a third section 250 coupled to an outlet of convection housing 230 to convey the working fluid from convection housing 230. In some open-loop configurations of system 200, such as the one shown in FIG. 4A, third section 250 of process line 234 may be configured to convey the working fluid to a heat exchanger 254, suchas an economizer, to transfer residual heat within the working fluid to a second portion of working fluid that is upstream of process line 234 or heater 210. In other open-loop variations, the working fluid may be conveyed from convection housing 230 to other components of the system, or an exhaust. In some closed-loop configurations of system 200, such as the one shown in FIG. 4B, third section 250 of process line 234 may be configured to convey the working fluid back to first section 242 of the process line (e.g., to be reheated in heater 210).

[0053] Bypass line 238 may include a first end coupled to first section 242 of process line and a second end coupled to second section 246 of the process line, such that a portion (up to all) of the working fluid travels through the bypass line instead of through heater 210. Bypass line 238 can be spaced from, insulated, or otherwise thermally decoupled from heater 210 such that fluids within the bypass line are not heated by heater 210. In some configurations, bypass line 238 may include a bypass valve 258 configured to selectively control an amount of working fluid (e.g., percentage of volume or mass of total process flow) that enters the bypass line. In some configurations, bypass valve 258 is connected to a controller (e.g., 220) and is configured to be actuatable via one or more signals initiated by the controller. As further described herein, bypass valve 258 can thus be actuated to maintain a desired temperature of the working fluid that enters convection housing 230. In this way and others, a temperature of the working fluid downstream from heater 210 can be maintained in a target range even while a temperature of the heater 210 varies.

[0054] Heater 210 can be any suitable heating device that is capable of heating a working fluid travelling through process line 234 to the desired temperature. In some configurations, heater 210 may be a radiator, electric heater, inductive heater, or the like. As depicted, heater 210 is configured to receive power from a power source 212, such as a renewable power source. Power source 212 may be configured to be actuated (e.g., via controller 220) to deliver electrical current to heater to generate heat at the heater. In some configurations, power source 212 can be configured to deliver power to heater 210 to keep the heater within an operating temperature range. The operating temperature range may have an upper limit that corresponds to the maximum allowable temperature of heater 210 (e.g., maximum operational temperature of the materials used in the heater). Additionally, or alternatively, the operating temperature range may have a lower limit that corresponds to a minimum temperature threshold that is set by the process requirements of the system. As an illustrative example, the operating temperature range may be equal to orbetween any two of the following: 1000, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, or 2200 °C. In some configurations, heater 210 is configured to store thermal energy that can be used at a later point. Examples of thermal storage systems that may be used for or in conjunction with heater 210 include the ETS Joule Hive Technology available from Electrified Thermal Solutions, Inc. (Medford, Massachusetts, USA), the Rondo Heat Battery available from Rondo Energy, Inc. (Alameda, California, USA), and others. Thus, when electrical power is available or relatively less expensive, thermal energy may be added to increase the temperature of a thermal mass of the heater, and the thereby stored for later use. When electrical power is not available or relatively more expensive, the stored thermal energy may be used to heat working fluids in the process line 234 (thereby reducing the temperature of the heater), without inputting any further electrical power.

[0055] System 200 may be operated based on a temperature of heater 210 to maintains a constant temperature working fluid to convection section 230 (and / or to radiant section 232a, as described below with reference to FIGs. 6A-6B). For example, a first portion of the working fluid can be directed through the heater to heat the first portion to or above a first temperature, and a second portion of the working fluid can be directed through the bypass to substantially maintain the second portion at a second temperature, such that when the two portions are mixed in second section 246 of process line 234, the working fluid portions combine to achieve a desired temperature of the combined working fluid. As an illustrative example, a controller (e.g., 220) may be configured to determine a temperature of heater 210 and a temperature of working fluid in first section 242 of process line; and, based on the determined temperatures and mass flowrate from process line 234, to actuate bypass valve 258 to maintain a temperature of the working fluid entering convection section 230 (and / or to radiant section 232a, as described below with reference to FIGs. 6A-6B) to be within a target temperature range. To further illustrate, for a given mass flowrate of gas through process line 234, when the temperature of the heater is relatively lower, then a relatively larger portion of the working fluid is directed through the heater to heat the working fluid to the desired temperature range. However, when the temperature of the heater is relatively higher, a relatively smaller first portion of the working fluid may be passed through the heater to heat the first portion to a temperature that is sufficiently high to — after the first portion is recombined with the second portion — result in a temperature of the recombined working fluid that is in the desired temperature range. Thus, as the temperature of heater 210 increases, bypassvalve 258 may be controlled to open and direct a relatively larger second portion (up to all) of the working fluid through bypass line 238 to maintain the temperature of the recombined working fluid that enters convection section 230.

[0056] In some configurations, system 200 can operate power source 212 and bypass valve 258 in conjunction to enhance the efficiency of the system. For example, power source 212 may be configured to deliver electricity to heater 210 (in a “charging mode”) based on a cost of electricity (e.g., from a power grid), availability of an energy supply (e.g., excess sunlight for solar panels, excess wind for wind power supplies, etc.), or associated thresholds. To further illustrate, controller 220 may actuate power source 212 to deliver electricity to heater 210 based on a cost of energy being below a first threshold or actuate the power source to terminate delivery of electricity to the heater based on a cost of energy being above a second threshold. In this way and others, heater 210 may be heated when electricity is relatively less expensive (e.g., a first timeframe) and the heat can still be delivered to a working fluid (in a “discharge” mode) when electricity is expensive and not delivered to the heater (e.g., a second timeframe). System 200 can be configured to charge and discharge heater 210 and operate bypass valve 258 to maintain a target temperature of the working fluid and to increase efficiency and lower cost of the system. Although described above with respect to electricity cost (e.g., from a power grid), system 200 can operate based on other factors or thresholds, such as availability of electrical power from a renewable energy source (e.g., solar or wind), excess energy capacity, or the like. For example, when renewable energy is available, such as from solar or wind generation, heating elements in heater 210 can be powered to both provide thermal energy to the gas passing through heater 210 and to simultaneously heat or charge heater 210 to store thermal energy; when renewable energy is less available or unavailable, some or all heating of the gas passing through heater 210 may come from the stored thermal energy.

[0057] The operations and functions disclosed herein can be implemented by a controller 220. For example, controller 220 may be configured to vary a current or voltage delivered to heater 210. Additionally, or alternatively, controller 220 may be configured to adjust an amount of power delivered between different supplies of power within power source 212 (e.g., renewable or nonrenewable). As an illustrative example, in configurations in which power source 212 includes a renewable energy supply and a non-renewable energy supply, controller 220 may be configured to utilize only the renewable energy supply unless an emergency event is triggered. For example,controller 220 may be configured to actuate the non- renewable energy supply based on heater 210 being below a minimum temperature threshold and the renewable energy supply being in an inactive state.

[0058] Controller 220 can include a processor and a memory connected to one or more described components or additional sensors, wireless interfaces, input / output (I / O) devices, or other circuitry or network components. The processor may be a central processing unit (CPU) or other computing circuitry (e.g., a microcontroller, one or more application specific integrated circuits (ASICs), and the like) and may have one or more processing cores. Memory may include read only memory (ROM) devices, random access memory (RAM) devices, one or more hard disk drives (HDDs), flash memory devices, solid state drives (SSDs), other devices configured to store data in a persistent or non-persistent state, or a combination of different memory devices. Memory 34 may store instructions that, when executed by processor, cause the processor to perform the operations described herein. The memory may be configured to store data associated with the system (e.g., 200), such as one or more measurements transmitted by sensors, one or more thresholds, other historical or predictive data, or combination thereof. Although described as a single controller / processor, controller 220 can include a plurality of components (controllers, processors, memories, transceivers, or the like) collectively working together to perform the operations disclosed herein. As an illustrative example, controller 220 can include a control room that is utilized by one or more operators. Further, although shown as being in wireless connection, controller 220 can be connected to the components of system 200 in any suitable manner (wired or wireless).

[0059] In some configurations, the working fluid may be a simulated combustion gas (SCG) with radiatively active species like CO2 or water to deliver heat by both radiation and convection. In some configurations, the SCG can be a gas comprising carbon dioxide, methane, water vapour, ozone, nitrogen oxides (e.g., nitrous oxide), chlorofluorocarbons (CFCs), halocarbons, certain organics such as volatile organic compounds, or combination thereof. In this way, system 200 may provide heat for both a radiation process and a subsequent convection process. For example, system 200 can include a heater 210 that is configured to heat gas (e.g., SCG) that is transported into an existing furnace system. In such configurations, the higher the temperature of the SCG, the more radiation it will give off. In some of the systems (e.g., 200) utilizing SCG, the system can provide heat transfer that is substantially entirely via radiation (e.g., heat transfer is performedby at least 90% radiation, such as greater than 91, 92, 93, 94, 95, 96, 97, 98, or 99% radiation). This can be particularly useful in retrofitting operations like the steam cracking process of FIGs. 1-3.

[0060] Referring now to FIG. 5, shown is another exemplary configuration of a system 200, which is similar to the example shown in FIG. 4B, except that in the configuration of FIG. 5, process line 234 passes through a non-operational radiant housing 232 to deliver the working fluid to convection housing 230. Radiant housing 232 may, for example, be a radiant housing of an existing fired heater that is configured to no longer combust fuel in the radiant section. For example, one or more burners or other combustion features can be deactivated and optionally removed. In some configurations, the radiant housing 232 is hollowed out (i.e., the burners and process tubes have been removed leaving just an empty box that leads to the convection section) and forms a portion of the process line 234 to allow working fluid to pass through a channel of radiant housing 232 and into a channel of convection section 230 to heat one or more heat exchanger 226 within convection section 230.

[0061] As depicted in FIG. 5, system 200 can include an additional housing 262 (e.g., radiant housing, heated tubular reactor) configured to heat a feedstock that would otherwise be typically heated (via combustion of fuel) in radiant section 232 of a conventional reactor furnace. For example, a second process line 266 can deliver the feedstock (e.g., hydrocarbons and steam) to a tubular reactor in housing 262. As shown, power source 212 may be connected to housing 262 to deliver electricity to housing 262 to add thermal energy to the feedstock in the reactor. For example, electrical current may be delivered directly to a conductive material of the tubular reactor for impedance or resistance heating, or may be delivered to one or more electric heating elements to radiatively heat the tubular reactor. As will be appreciated by those of ordinary skill in the art, one of the functions often performed in convection section 230 of such a system is the preheating of a feedstock for delivery to the tubular reactor (conventionally disposed in a radiant housing 232). In the depicted embodiment, heat exchangers in convection section 230 can continue to be used for such purposes. For example, process line 266 may receive preheated feedstock after the feedstock has passed through one or more heat exchangers 226 in convection section 230.

[0062] Referring now to FIGs. 6A and 6B, a further configuration 200a of the present systems is shown. As shown, system 200a includes an operational radiant housing 232a that is in communication with a convection housing 230. System 200a is more similar than the foregoingvariations of system 200 to conventional steam cracking systems in that process line 266 of system 200a delivers feedstock into a tubular reactor of an operational radiant section 232a, which is coupled to convection section 230 such that hot gases are conveyed from radiant section 232a into convection section 230. However, radiant section 232a differs from prior systems in that radiant section 232a is not heated by combustion of fuel.

[0063] Instead, and as shown in more detail in FIG. 6B, radiant housing 232 one or more electric heating elements 274 configured to radiantly heat the tubular reactor in the radiant housing, and a plurality of openings 278 through which hot gases (e.g., SCG) from heater 210 are delivered into the interior of the radiant housing also to heat the tubular reactor in the radiant housing. In this configuration, heated gas (SCG) from section 246 of process line 234 can provide some of the thermal energy utilized in the radiant section to heat the thermal reactor (and feedstock therein), and thereby offset a portion of the amount of electrical power that would otherwise be needed for heating elements 274 to provide sufficient thermal energy to heat the tubular reactor of the radiant section. For example, the SCG entering the radiant section may provide up to 75% (e.g., between any two of 10%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, and / or 75%) of the heating duty needed for the tubular reactor in the radiant section.

[0064] As shown, heating elements 274 can, for example, be disposed on one or more walls 270 of the radiant housing. Wall(s) 270 can include any suitable material and, in some configurations, may include one or more of the materials used in heater 210 and / or the heating element(s) may be incorporated into the wall itself. Wall(s) 270 may be a wall of a preexisting radiant section in which burners are removed and the wall is modified or replaced while leaving the rest of the radiant housing structurally the same (or at least with minimal further modification). For example, wall 270 itself can include conductive refractory bricks that are configured to receive electrical current and convert the current to heat, as described above.

[0065] In this configuration, with heat in the radiant section provided both by the SCG and by the heated elements, these two sources can be controlled (e.g., by controller 220) to maximize operating efficiency or cost. For example, in the depicted configuration, heated SCG can come from a heat storage device (heater 210) that can continue to deliver hot SCG even when renewable energy is unavailable and / or electricity from the grid is relatively expensive. For example, when renewable energy is available and / or electricity is available from the grid at a relatively low cost, more power can be delivered to heating element(s) 274 to provide a greater portion of thermalenergy required for the radiant section, and the available renewable energy and / or relatively lower cost electricity from the grid can be used to charge or heat the heat storage device (heater 210) to store thermal energy. Conversely, when renewable energy is unavailable and / or electricity from the grid is relatively more expensive, the stored thermal energy from heater 210 can be used to heat the SCG and the the hot SCG can provide a greater portion of the thermal energy needed for the radiant section. Thus, by adjusting the proportions of thermal energy respectively provided by heating elements 274 and the SCG, the overall cost and reliability of the heater can be optimized.

[0066] Opening(s) 278 can include or be configured to receive tubes and / or nozzles that are configured to deliver hot gas (e.g., a SCG) from section 246 of process line 234 (e.g., via a manifold) into radiant housing 232 at a temperature (e.g., 1,400-2,000 °C) similar to that of flames used to heat conventional radiant sections of such systems. As a non-limiting example, SCG can be transmitted from heater 210, through second section 246 of process line 234, and into radiant housing 232a at or above a first temperature threshold (e.g., 1800, 1900, 2000 °C or higher) to heat the tubular reactor in radiant housing (and feedstock passing through the tubular reactorvia process line 266. The SCG then passes through radiant housing 232a and into a chamber of convection housing 230 at or above a second temperature threshold (e.g., 1000, 1200, 1400 °C or higher) to provide thermal energy to heat exchangers 226 in convection section 230. Accordingly, system 200 can be suitable for retrofitting existing structures and furnaces for use without combustible fuels that emit CO2 or other greenhouse gasses. As described above, power source 212 can be configured to be connected to heater 210, one or more elements of radiant housing 232a (e.g., heating elements), or both. As described above, heater 210 and bypass valve 258 may be controllable to adjust a temperature of a working fluid entering radiant housing 232a.

[0067] Referring now to FIG. 7A-9B, three illustrative, non-limiting variations of a heater 210 of the present disclosure are shown, each coupled to a power source 212 that may be utilized in a heat production system 200 (several variations of which are described above with reference to FIGs. 4A-4B, 5, 6A-6B). However, in other configurations, other heaters (e.g., electrical heaters) may be used in place or in in conjunction with heater 210. Generally, heater 210 (e.g., stack 210) includes a mass of material that is stable at high temperatures, and that is configured to be electrically heated to increase the temperature of the stack 210 and thereby store thermal energy for later use (e.g., when electrical power is less available, unavailable, or relatively more expensive).

[0068] In the depicted variations, stack 210 includes a body 214 and a plurality of tubes 218 (e.g., between 2 and 100 tubes, or more) extending through the body to facilitate radiative heat transfer from the body to the tubes. For example, tubes 218 may be disposed or suspended relative to the body (e.g., such that the tubes, or at least a majority of the tubes, do not directly contact the body). In particular, FIGs. 7A and 7B depict a first example of stack 210 in which body 214 defines individual gaps or passages 216 each with a closed cross-section to receive a single tube 218. In other variations, the body can instead define one or more enclosed gaps or passages 216 each sized to receive two or more tubes 218. For example, FIGs. 8A and 8B depict a second example of stack 210 in which body 214 includes a plurality of independent segments (or walls) that are disposed relative to one another to define gaps or passages 216 that do not individually have cross-sections that are closed by body 214 itself. In each of the depicted examples, tubes 218 are positioned so that they are in a line-of-sight of body 214 such that the tubes (or any fluid disposed therein) are configured to absorb thermal radiation (e.g., infrared light) emitted from the body.

[0069] FIGs. 9A-9B depict a third configuration in which conduits 218 are omitted such that gas flows directly through gaps or passages 216. This configuration allows the gas to contact the material of body 214 such that heat can trasnfer convectively between the gas and body 214, rather than radiatively between body 214 and conduits 218 as in the above configurations.

[0070] Stack 210 is not intended to be limited by the depicted examples and may include other suitable geometries that are known in the art. For example, body 214 may include any number of segments or other connecting structures and the body (e.g., gaps defined therein), tubes 218, or both, can be rectangular, triangular, hexagonal, or otherwise polygonal, circular, semi-circular, elliptical, or otherwise rounded, star-shaped, honeycomb-shaped, or other suitable shape. For example, in other variations, stack 210 may itself define conduits or flow paths to convey the fluid through the stack such that the fluid is not separated from the body as it flows through the body.

[0071] Body 214 can comprise a material that is physically stable at high temperatures and adapted for thermal storage, such as fire brick, ceramic bricks, and / or other refractory materials. For example, body 214 may include a plurality of refractory bricks. In some configurations, body 214 may include a plurality of conductive refractory bricks that are configured to pass electric current for resistive heating and, in some configurations, a combination of such conductive refractory and non-conductive refractory bricks. In configurations that include a combination ofconductive refractory bricks and non-conductive refractory bricks, the conductive refractory bricks conduct electric current to resistively convert electrical energy to thermal energy and thereby directly heat the conductive refractory bricks and indirectly heat the non-conductive refractory bricks (which are in thermal communication with the conductive refractory bricks). In some configurations, body 214 can be configured to operate at temperatures up to 2000 °C or greater and much higher than the operating temperatures of conventional electrical heating elements (e.g., Kanthal - FeCrAl alloys or Fe-like, Cr-like, Al-like metallic elements or alloys thereof).

[0072] In some configurations, the conductive refractory bricks include a conductive refractory material or may be doped with a conductive material (e.g., metal oxide) such that electrical current will flow through the brick, but with sufficient resistance to convert electrical energy to thermal energy and thereby heat the brick for storage of thermal energy. As used in this disclosure, “conductive refractory material” is a material that itself conducts electricity such that electrical current flowing through the material itself generates thermal energy (e.g., converts electrical energy to thermal energy) — i.e., the conductive refractory material does not include separate heating elements. The use of conductive refractory bricks allows the stack to omit conventional heating metal elements, such as wires or ribbons, which are typically more susceptible to oxidation and other degradation at elevated temperatures (and are therefore not suitable for use at temperatures comparable to those produced by conventional burners.

[0073] In configurations that include both conductive refractory bricks and non-conductive refractory bricks, the non-conductive refractory bricks are thermally coupled to the conductive refractory bricks to absorb the heat generated by the conductive refractory bricks to heat body 214 and thereby store thermal energy for later use. Both conductive and non-conductive bricks can include a material having both a relatively high emissivity (e.g., 0.5 or greater, 0.7 or greater, or 0.8 or greater) for efficient emission of thermal radiation to tubes 218 and relatively high specific heat (e.g., 400 J / kg-K or greater, 450 J / kg-K or greater, or 500 J / kg-K or greater) to increase the thermal energy the stack 210 can temporarily “store” as thermal energy is dissipated. In some configurations, the non-conductive refractory bricks are configured to store or hold heat and may have a specific heat that is higher than the non-conductive refractory bricks.

[0074] In some configurations, body 214 may contain sequential section of heat storage material and also sections with heating elements (e.g., an inlet section with heating elements that heats gas entering body, and a subsequent or down-stream storage section into which heated gasflows from the inlet section). In such configurations, the heated elements are not in direct thermal communication with the heat storage material. Instead, electricity is applied to the heating elements which in turn heat the gas, such that the gas can in turn heat the storage material. In such configurations, heat can be transferred from hot gas to storage material when renewable energy is available and / or electricity from the grid is relatively less expensive; and, when renewable energy is not available and / or electricity from the grid is relatively more expensive, thermal energy can be transferred from the storage material to the gas.

[0075] Body 214 is configured, via the conductive refractory bricks, to receive external power (e.g., from power source 212) and convert electrical energy to thermal energy that heats the material of the stack and thereby “stores” the thermal energy to be later radiatively or convectively, depending on design, “discharged” to heat a working fluid that is fed through tubes 218. This capability can allow stack 210 to be charged and discharged at different times, which can be particularly advantageous. For example, utilities may offer discounts to customers that can be flexible in their consumption demands during peak hours when electricity production or grid capacity are stressed. Thus, system 200 may be configured to store energy and then use this stored energy later when other energy from external sources (e.g., grid, solar, wind or the like) is more expensive (e.g., peak grid hours) or of limited availability (e.g., dark hours for solar or still hours for wind). In this way and others, system 200 can maintain operations despite temporary interruptions of power.

[0076] Tubes 218 each define a passageway that is configured to transport a gas through body 214 to heat up the gas. Tubes 218 may comprise a suitable material to absorb thermal radiation (e.g., via radiation) from body 214 and transfer thermal energy to the fluid flowing through the tubes. In some configurations, tubes 218 comprise a material with relatively high emissivity (e.g., 0.5 or greater, 0.7 or greater, or 0.8 or greater) such as any of various metal alloys. In some configurations, exterior surfaces of at least some of tubes 218 (or portions of tubes) can be polished, coated, or both to increase absorptivity.

[0077] Power source 212 is configured to deliver electrical current to stack 210. In some configurations, the electrical power from the power source 212 may correspond to a voltage greater than 500 volts, preferably greater than 1000 volts, and more preferably greater than 2000 volts. Power source 212 can include one or more wires or other conductors that are configured to deliver electricity to one or more conductive refractory bricks within body 214. In some configurations,power source 212 may include a source of renewable energy such as solar, wind, geothermal, hydropower, biomass, or other renewable sources. In some configurations, power source 212 may include only renewable energy supplies and, in other configurations, the power source may include a combination of renewable energy and non-renewable energy supplies. In an illustrative, nonlimiting example, power source 212 may include a plurality of solar panels and can be configured to deliver electricity to stack 210 during the daytime. In such an example, system 200 and stack 210 can be configured to “store” heat during the daytime and “discharge” heat during the night to continue operations until the sun rises again. Power source 212 can include or be connected to a controller 220 that is configured to actuate the power source and control the power delivered from the power source to stack 210 based on one or more conditions or events.* * *

[0078] 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.

[0079] 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 for heating a chemical process, the system comprising: a thermal mass configured to store thermal energy; a heater configured to heat the thermal mass; where the thermal mass is configured to heat a gaseous working fluid as the working fluid flows in thermal communication with the thermal mass; and a furnace comprising a convection section configured to receive the heated working fluid from the heater to transfer thermal energy from the working fluid to at least one heat exchanger disposed within the convection section.

2. The system of claim 1, where the furnace further comprises: a radiant section comprising a tubular reactor and one or more electric heating elements, the radiant section configured to receive the heated working fluid such that the tubular reactor is heated by a combination of thermal energy provided by the heating element(s) and thermal energy provided by the working fluid; where the convection section is configured to receive the heated working fluid through the radiant section.

3. The system of any of claims 1-2, wherein the working fluid comprises one or more radiatively active species, selected from a list of radiatively active species consisting of: carbon dioxide, methane, water vapour, ozone, and nitrous oxide.

4. The system of any of claims 1-3, where the heater comprises a plurality of electric heating element.

5. The system of claim 4, where the heating elements are in direct thermal communication with the thermal mass.

6. The system of any of claims 1-5, where the thermal mass defines a plurality of passages configured to receive working fluid such that the thermal mass is configured to contact and convectively heat the working fluid.

7. The system of any claims 1-5, where the thermal mass comprises a plurality of conduits distinct from the thermal mass and configured to receive working fluid such that the thermal mass is configured to radiatively heat the conduits.

8. The system of any of claims 1-7, comprising: a process line in fluid communication with upstream and downstream sides of the thermal mass; a bypass line in communication with the process line upstream and downstream of the thermal mass such that the bypass line is configured direct a portion of the working fluid around the thermal mass; and a bypass valve that is actuatable to control the respective amounts of working fluid from the process line that are delivered to: the bypass line; and the thermal mass.

9. A method of retrofitting a combustion furnace to be electrically heated, the method comprising: discontinuing, at a fired furnace having a radiant section and a convection section, operation of one or more gas burners configured to ignite a combustible gas within the radiant section; providing a thermal mass in a process line that is configured to deliver a gaseous working fluid to the radiant section and through a convection section of the furnace, the thermal mass coupled to a heater that is configured to receive electricity from a renewable power source to generate and store thermal energy; and conveying the working fluid through one or more gaps or passages of the thermal mass to heat the working fluid, and conveying the working fluid from the thermal mass to convection section of the furnace to heat at least one heat exchanger disposed within the convection section.

10. The method of claim 9, further comprising:installing an electrically heated tubular reactor and configuring a process line to deliver a feedstock to the electrically heated tubular reactor.

11. The method of claim 9, further comprising: installing one or more electric heating elements in the radiant section; and configuring the radiant section to receive the heated working fluid from the thermal mass such that the heated working fluid first adds thermal energy to a tubular reactor in the radiant section and is then conveyed to the convection section of the furnace.

12. A process for operating a convection section of a chemical production system without combustion of hydrocarbons in a radiant section of the system, the process comprising: heating a gaseous working fluid by conveying the working fluid through one or more gaps or passages defined in a body of a thermal mass that is coupled in thermal communication with a heater that is configured to heat the thermal mass; and conveying the heated working fluid from the thermal mass to the convection section to provide thermal energy to one or more heat exchangers disposed within the convection section.

13. The process of claim 12, wherein conveying the working fluid to the convection section comprises: powering electrical heating elements in a radiant housing defining a radiant section to heat a tubular reactor within the radiant housing; where the working fluid is conveyed to the convection section via the radiant section such that the working fluid provides thermal energy to heat the tubular reactor before the working fluid reaches the radiant section.

14. The process of any of claims 12-13, further comprising: adjusting a bypass valve to convey working fluid through a bypass line that bypasses the thermal mass.

15. The process of any of claims 12-14, wherein the working fluid comprises one or more radiatively active species, selected from a list of radiatively active species consisting of: carbon dioxide, methane, water vapour, ozone, and nitrous oxide.

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