Electrical gas-heating installation, in particular for a steam cracking furnace

Abstract

The invention relates to an electrical gas-heating installation (1), in particular for heating an oxidising gas supplying a steam cracking furnace. The installation comprises in particular, mounted in series on a gas supply pipe (3): - a first electric heating system (10), - a second electric heating system with thermal store (20) equipped with at least one thermal store device (210) containing at least one thermal storage medium chosen from a solid medium and a liquid medium and at least one heating device (220) for heating the thermal storage medium. A management system (40) is configured so that, in a charging phase, the thermal storage medium is heated so that it accumulates heat energy and the gas is heated by means of the first electric heating system and, in a discharge phase, the heat energy accumulated by the thermal storage medium is transferred to the gas.

Description

ELECTRICAL INSTALLATION FOR GAS HEATING, PARTICULARLY FOR A STEAM CRACKLING FURNACE Technical field of the invention

[0001] The present invention relates to an electric gas heating system, particularly for heating the combustion gas of a steam cracking furnace fed with combustion gas. The invention also relates to a hydrocarbon steam cracking system and process using the electric heating system according to the invention. Technological background

[0002] The steam cracking process of hydrocarbons allows the production of light olefins, and more specifically ethylene and propylene. It consists of thermally cracking a mixture of hydrocarbons and steam in one or more reactors at high temperatures of around 800 to 850°C and under low pressures (1 to 3 bar) to break carbon-hydrogen and / or carbon-carbon bonds and produce unsaturated hydrocarbons within the reactor(s). The effluents exiting the reactor(s) are then quenched in one or more heat exchangers, generally designated by the acronyms TLX or TLE (Transfer Line Exchanger), to limit secondary reactions such as the polymerization of olefins, dienes, and acetylenes. The cooled effluents are then fractionated.A steam cracking process thus requires inputs of heat (injection of energy to increase the temperature and provide the enthalpy of reaction) and cold (extraction of energy to lower the temperature) to fractionate and significant amounts of energy, a large part of which is currently supplied by fossil energy.

[0003] Increasing environmental concerns, however, require replacing this fossil energy with decarbonized energy (without CO2 emissions) and in particular renewable energy, especially renewable electricity produced by wind turbines and / or solar panels.

[0004] One of the heat inputs required for a steam cracking process is the heating of the combustion air for the burners in a steam cracking furnace. To minimize the amount of fuel needed to provide thermal energy to the material being cracked, the combustion air must enter the burners at a temperature above 200 °C, typically between 300 and 600 °C. Heating this combustion air electrically is possible but expensive, especially when electricity costs are high.

[0005] There is therefore a need to heat a gas, and in particular the combustion gas of a steam cracking furnace or any other combustion system, to a high temperature while reducing the economic, energy and environmental impact.

[0006] To this end, the invention proposes an electrical gas heating installation implementing an electric heating system with thermal storage.

[0007] A first object of the invention relates to an electric gas heating installation comprising: - at least one gas supply line, - a first electric heating system, mounted on at least one gas supply line, - a second electric heating system with thermal storage mounted on at least one gas supply line, downstream of the first heating system with respect to the gas flow, and comprising: - at least one thermal storage device containing at least one thermal storage medium selected from a solid medium and a liquid medium, - optionally at least one heating device for at least one thermal storage medium, and further comprising: - according to a first configuration (i) a bypass circuit of at least one gas supply line passing through at least one thermal storage device containing only at least one solid medium,or- according to a second configuration (ii) a heat exchanger in which the liquid medium and the gas supplied by at least one supply line circulate, and a circuit in which the liquid medium circulates, this circuit comprising at least one thermal storage device and the heat exchanger.

[0008] The electric heating installation according to the invention further comprises a management system for the first and second electric heating systems, configured, in particular programmed, to: (a) in a charging phase in which at least one thermal storage medium of the second heating system accumulates heat, operate the first heating system to heat the gas to a first temperature T1, and (a1) operate the heating device to heat at least one thermal storage medium, and / or (a2) use at least a fraction of the gas heated by the first heating system to heat the thermal storage medium, (b) in a discharging phase in which at least one thermal storage medium of the second heating system releases heat, control the shutdown of the optional heating device, operate the first heating system to heat the gas to a second temperature T2,and: in the first configuration (i) circulate the entire gas flow at the second temperature T2 through the bypass circuit via the thermal storage device containing the solid medium to heat the gas from the second temperature T2 to a predetermined temperature Tp, or circulate a fraction of the gas flow at the second temperature T2 through the bypass circuit via the thermal storage device containing the solid medium to heat this gas fraction to a third temperature T3, which, when mixed with the remaining fraction of the gas flow, reaches the predetermined temperature Tp, or in the second configuration (ii) circulate the liquid medium through at least one thermal storage device and then through the heat exchanger to heat the gas from the second temperature T2 to the predetermined temperature Tp.

[0009] This arrangement allows the charging phase to be implemented while electricity is cheaper and / or comes from decarbonized sources (wind, solar, nuclear power plant, hydroelectric, etc.), which makes it possible to decarbonize the electrical consumption of the installation and / or reduce operating costs.

[0010] The predetermined temperature Tp can be equal to or less than a target temperature Tc. The target temperature Tc is defined as a temperature to be reached at the outlet of the installation according to the invention. This target temperature Tc can be determined based on the intended use of the installation according to the invention.

[0011] The first temperature T1 may be greater than or equal to the predetermined temperature Tp or the target temperature Tc, or be less than either. During the charging phase, when case (a2) is in and at least a fraction of the gas heated by the first heating system is used to heat the thermal storage medium, the temperature T1 is advantageously greater than a storage temperature, the latter advantageously being greater than the predetermined temperature Tp or the third temperature T3, and preferably greater than the target temperature Tc.

[0012] The second temperature T2 is typically lower than the predetermined temperature Tp. The third temperature T3 is typically higher than the second temperature T2 and lower than the predetermined temperature Tp or the target temperature Tc.

[0013] Generally, during the charging phase, at least one thermal storage medium is heated to a storage temperature Ts (the temperature reached by at least one thermal storage medium at the end of the charging phase). This storage temperature Ts can advantageously be higher than the predetermined temperature or the target temperature, or even higher than the third temperature T3 used in the discharge phase in the first configuration (i). During the discharge phase, the at least one thermal storage medium at temperature Ts can then heat the gas from the second temperature T2 to the predetermined temperature Tp or to the third temperature T3, depending on the configuration, as explained previously.

[0014] Advantageously, the heating device of the second thermal heating system can be an electric heating device, such as a Joule effect, induction, microwave, plasma, shock wave heating device or a combination of these devices, preferably a Joule effect and / or induction heating device.

[0015] Advantageously, the first electric heating system may include one or more of the following components mounted in series and / or in parallel on at least one gas supply line: - a heat pump connected on one side to the gas supply line so as to transmit heat to it, and on the other side to a line in which a hot fluid circulates so as to receive heat from the latter, - a mechanical vapor recompression system, comprising at least one mechanical steam compression stage, at least one first heat exchanger receiving steam produced by at least one mechanical compression stage and connected to the gas supply line so as to transmit heat to it, a second heat exchanger receiving heat from a hot fluid and producing steam supplying at least one mechanical compression stage, - an electric heating device.

[0016] Preferably, the first electric heating system includes at least one heat pump connected on one side to the gas supply line so as to transmit calories to it and on the other side to a line in which a hot fluid circulates so as to receive calories from the latter.

[0017] The electric heating system can be as described previously. It is advantageous to use one or more heat pumps (in series and / or parallel) followed by one or more electric heating devices, or one or more electric heating devices. Most often, the first electric heating system comprises two or three of these components connected in series, for example, a heat pump followed by at least one electric heating device, most often two or three. Using a heat pump allows the use of a hot fluid or waste heat from a unit, for example, a steam cracker or any other heat-producing unit. A heat pump also minimizes the electricity consumption associated with the heating operation by utilizing a waste heat source, either directly or via a heat transfer fluid.

[0018] In a first embodiment, in the first configuration, the second electric heating system may include: - the bypass circuit comprising at least one thermal storage device containing only the solid medium and, - at least one heating device for the solid medium, optionally mounted on a bypass pipe connected to the bypass circuit in parallel with at least one thermal storage device.

[0019] Preferably, the second electric heating system can then include a single thermal storage device.

[0020] The management system can then be further configured to operate the second heating system in the following manner, and in particular to: In a charging phase, (a1) circulate gas through at least one thermal storage device and operate the heating device of the second heating system, and / or (a2) operate the first heating system to heat the gas to the first temperature T1 and use at least a fraction of the gas to heat the thermal storage medium; In a discharging phase, circulate the gas through at least one thermal storage device, the heating device of the second heating system being off.

[0021] In this embodiment and its variants, the management system can also be configured to operate the first heating system as previously described.

[0022] In this first embodiment of the first configuration, the electric heating installation according to the invention can then include a third electric heating system mounted on the gas supply line, in parallel with the second electric heating system. This is particularly advantageous when, during the charging phase, the gas is heated by the first heating system to a first temperature T1 that is lower than the target temperature Tc.

[0023] The management system can then be further configured to: In the charging phase operate the first and third electric heating systems to heat the gas to the predetermined temperature Tp, In the discharging phase, operate the first electric heating system to heat the gas to the second temperature T2, in particular lower than the predetermined temperature Tp, then circulate all or a fraction of the gas flow through the thermal storage device to heat all of the gas flow to the predetermined temperature Tp or to heat the fraction of the gas flow to the third temperature T3 which, in mixing with the remaining fraction of gas flow, reaches the predetermined temperature Tp.

[0024] Preferably, this third thermal heating system may include one or more electric heating devices, for example, a single one. This electric heating device may be as previously defined.

[0025] In a second embodiment, in the second configuration, the circuit in which a liquid medium circulates may include at least one thermal storage device, the heat exchanger and the liquid medium heating device.

[0026] The management system can then be further configured to operate the second heating system, and in particular to: In a charging phase, (a1) circulate the liquid medium in this circuit and operate the heating device to heat it before it enters at least one thermal storage device, and optionally (a2) operate the first heating system to heat the gas to the first temperature T1 and use at least a fraction of the gas to heat the thermal storage medium via the heat exchanger, In a discharging phase, circulate the liquid storage medium in this circuit, and command the shutdown of the heating device.

[0027] In this embodiment and its variants, the management system can also be configured to operate the first heating system as previously described.

[0028] In a variant of this second embodiment, the circuit of the second electric heating system may include a single thermal storage device. The liquid medium heating device may then be installed on a bypass line mounted in parallel with the thermal storage device or integrated into it (the bypass line is then omitted). During the charging phase, the liquid medium may then circulate in a loop formed by the bypass line on which the heating device and the thermal storage device are installed, while during the discharging phase, the liquid medium circulates in a loop formed by the circuit containing the thermal storage device and the heat exchanger. Note that the thermal storage device may also contain a solid medium.An advantageous use can be made of a thermal storage device containing layers of liquid thermal storage media at different temperatures, with the temperature of the layers increasing from bottom to top.

[0029] In another variant of the second embodiment, in the second configuration, the circuit may comprise, connected in series in the direction of liquid medium flow, a first thermal storage device, a second thermal storage device, and the heat exchanger, with at least one liquid medium heating device integrated into each thermal storage device or located between the first and second thermal storage devices. During the charging phase, the liquid medium then circulates in a loop comprising the two thermal storage devices and the heating device(s): the liquid medium in a cooler thermal storage device is heated by the heating device before being stored in the warmer thermal storage device.During the discharge phase, the liquid medium circulates through the circuit from the hottest storage device to the heat exchanger, while the heating system is off. The control system can then be configured to operate the second heating system as previously described.

[0030] In a third embodiment, in the second configuration, the circuit may include, connected in series in the direction of liquid flow, a first thermal storage device, optionally a second thermal storage device, and the heat exchanger. At least one liquid medium heating device is mounted on at least one gas supply line, upstream of the heat exchanger of the second electric heating system. The gas heated by this heating device then heats the liquid medium during the charging phase via the heat exchanger. During the discharging phase, this heating device is switched off. The control system can then be configured to operate the second heating system as previously described.In this embodiment and its variants, the management system can also be configured to operate the first heating system as previously described.

[0031] When the second electric heating system operates with a liquid thermal storage medium, in the second configuration, the installation according to the invention may advantageously include a third electric heating system mounted on at least one gas circulation line downstream of the heat exchanger of the second electric heating system. This third electric heating system can advantageously be used during the charging phase to maintain the liquid medium circulating in the heat exchanger at an operating temperature, for example, a temperature at which it is liquid. It can also allow the gas to reach the target temperature Tc during the charging phase when the initial temperature T1 at the outlet of the first electric heating system is insufficient (i.e., below the target temperature).

[0032] The electric gas heating system according to the invention can be used in any gas system that requires or benefits from heating, such as a combustion system, for example, a combustion furnace or a combustion boiler, or, more generally, any combustion system comprising at least one fuel gas supply line and at least one combustion gas supply line. The system according to the invention can then be mounted on at least one combustion gas supply line of such a combustion system to preheat the gas before it enters a combustion zone of the combustion system.

[0033] The electrical gas heating system according to the invention can advantageously be integrated into a hydrocarbon steam cracking furnace comprising a radiant heating zone equipped with burners connected to at least one fuel gas supply line and at least one oxidizing gas supply line. The system according to the invention is then mounted on at least one oxidizing gas supply line to heat the oxidizing gas before it enters the furnace.

[0034] The invention also relates to a steam cracking installation comprising a steam cracking furnace, the steam cracking furnace and an electrical heating installation according to the invention, the furnace comprising a radiation zone equipped with burners connected to at least one fuel gas supply line and to at least one oxidizing gas supply line and the installation according to the invention being mounted on the latter.

[0035] The invention also relates to a process for steam cracking hydrocarbons characterized in that it comprises: - a cracking step of a hydrocarbon feedstock carried out at a cracking temperature in a steam cracking plant according to the invention, this cracking temperature being obtained by the combustion in the burners of the steam cracking furnace of a mixture of combustion gas and hot oxidizing gas, in which the heating of the oxidizing gas before its entry into the burners is carried out by the electric gas heating plant according to the invention and comprises: - supplying the first electric heating system with gas to be heated, optionally, the oxidizing gas entering the first electric heating system being at a temperature ranging from ambient temperature to 280 °C, and - in a charging phase in which the thermal storage medium of the second heating system accumulates heat,operate the first heating system to heat the gas to a first temperature T1, and (a1) operate the heating device to heat the thermal storage medium, and / or (a2) use at least a fraction of the gas heated by the first heating system to heat the thermal storage medium, - in a discharge phase in which the thermal storage medium of the second heating system releases heat, command the shutdown of the optional heating device, operate the first heating system to heat the combustion gas to a second temperature T2, and, in the first configuration (i) circulate the entire gas flow at the second temperature T2 through the bypass circuit via the thermal storage device containing the solid medium and heat the gas from the second temperature T2 to a predetermined temperature Tp, or ,circulate a fraction of the gas flow at the second temperature T2 in the bypass circuit through the thermal storage device containing the solid medium to heat this gas fraction to a third temperature T3, which, mixing with the remaining fraction of the gas flow, reaches the predetermined temperature Tp, or in the second configuration (ii) circulate the liquid medium through at least one thermal storage device and then into the heat exchanger to heat the combustion gas from the second temperature T2 to the predetermined temperature Tp.

[0036] The steam cracking furnace, installation, and process according to the invention are particularly well-suited for the steam cracking of ethane but can also be used for the steam cracking of other hydrocarbon feedstocks such as liquefied petroleum gases (propane, butane), naphtha, diesel fuel, and vacuum distillates. Other hydrocarbon feedstocks may include hydrocarbons of biological origin, such as ethane, propane, butanes, naphtha, and distillates produced during the hydrotreating / hydrocracking of fatty acid esters (e.g., triglycerides), biomass pyrolysis oils, or biomass hydrothermal liquefaction oils. Other hydrocarbon feedstocks may be hydrocarbons obtained by pyrolysis, hydrothermal liquefaction, or hydrocracking of plastic waste. Detailed description of the invention Description of the figures

[0037] The invention is now described with reference to the accompanying, non-limiting drawings, in which:

[0038] The diagram schematically represents an electrical installation for heating a gas and a steam cracking furnace according to an embodiment of the invention.

[0039] Lare represents schematically an electrical installation for heating a gas and a steam cracking furnace according to another embodiment of the invention.

[0040] Lare represents schematically an electrical installation for heating a gas and a steam cracking furnace according to another embodiment of the invention.

[0041] Lare represents schematically an electrical installation for heating a gas and a steam cracking furnace according to another embodiment of the invention.

[0042] In the figures, the same elements are designated by the same references.

[0043] The terms "upstream" and "downstream" are used in relation to the flow of fluids, symbolized by arrows in the figures.

[0044] The various units of a steam cracking plant include many components requiring either an electrical power supply, a thermal power supply, or both.

[0045] In particular, the steam cracking furnace, also called a steam cracking reactor, includes supply lines for the fluids entering the steam cracking reactor(s) and sections for heating the fluids and / or producing steam entering the reactor(s).

[0046] The thermal energy required for the steam cracking reaction is supplied by the combustion of combustible gas with an oxidizer (air, etc.). Approximately 40 to 50% of the heat of combustion is absorbed in a radiant zone of the steam cracking furnace, while the remainder passes to a convection zone where the majority of the sensible heat from the combustion gases is exchanged to preheat hydrocarbons and / or water and / or steam via at least one heat exchanger.

[0047] In the present invention, the oxidizing gas, typically air, supplying the burners of the steam cracking furnace is heated by means of an electric heating installation according to the invention.

[0048] The diagram schematically represents an electrical heating installation according to an embodiment of the invention, here allowing the heating of a combustion gas supplying a steam cracking furnace, in which a steam cracking step takes place.

[0049] Typically, a steam cracking furnace 110 comprises a lower radiant section 110a and an upper convection section 110b. The heat from the radiant section 110a is supplied by the combustion of a fuel (generally combustible gas, such as methane or H2) in the presence of an oxidizer (air, etc.) in at least one burner. The steam cracking furnace 110 thus includes one or more fuel supply lines 2 and one or more oxidizer supply lines 3 leading to one or more burners. Combustion takes place in one or more burners located in the base, the ceiling, and / or the side walls of the lower part of the furnace enclosure 110.

[0050] The hydrocarbon feedstock and dilution steam are injected into at least one heat exchanger tube bundle (not shown) located in the convection zone 110b. The hydrocarbon feedstock and dilution steam may be preheated separately and then mixed and further preheated in the at least one heat exchanger tube bundle, typically to a temperature between 600 and 680°C. This mixture is then distributed into one or more tube reactors (not shown) located in the radiation zone 110a. Burners in the radiation zone further heat the tube reactors to initiate thermal cracking. The effluent temperature at the outlet of the tube reactors is typically between 800 and 900°C.

[0051] According to the invention, the combustion gas supply line 3 is equipped with an electric heating installation 1 comprising a first electric heating system 10 and a second electric heating system 20 connected in series in the direction of combustion gas flow. The installation 1 according to the invention thus comprises a portion of the combustion gas supply line 3, which may be connected to it or form part of it.

[0052] The first electric heating system 10 may include one or more components selected from a heat pump and an electric heating device connected in series and / or parallel. However, the use of at least one heat pump is preferred. In the example shown, the first electric heating system 10 includes a heat pump PACH. In this example, the heat pump comprises a circuit 100 in which a working fluid circulates, preferably a gas (e.g., CO2, a hydrocarbon, in particular an alkane such as pentane, water, ammonia, a refrigerant such as a hydrofluoroolefin or HFO, or a hydrochlorofluoroolefin or HCFO, etc.) equipped with two heat exchangers Ech_1 and Ech_2. The heat pump also typically includes a compressor and an expansion device (calibrated orifice, electronic expansion valve, turbine, semi-closed valve, etc.), which are not shown.The working fluid circulating in the first heat exchanger Ech_1 transfers heat to the combustion gas circulating in the first heat exchanger Ech_1 and supplied by the combustion gas supply line 3, while the working fluid circulating in the second heat exchanger Ech_2 receives heat from at least one hot fluid circulating in the second heat exchanger and originating, for example, from the steam cracking plant to which the furnace belongs. This hot fluid circulating in a line 4 can, for example, come from the steam cracking plant's water quenching tower, or from ambient air, a geothermal source, the sea, or a return water from a cooling unit.

[0053] As a replacement for the PACH and / or the electric heating device, or in combination with it and / or with the electric heating device, the first heating system may include a mechanical vapor recompression (MVR) system, comprising one or more mechanical steam compression stages, one or more first heat exchangers receiving steam produced by one or more of the mechanical compression stages, for example downstream of each stage, and connected to the gas supply line so as to transmit heat to it, a second heat exchanger receiving heat from a hot fluid and producing steam (low pressure or vacuum steam) supplying the mechanical compression stage(s).

[0054] The second electric heating system20 is an electric heating system with thermal storage, comprising here:

[0055] - at least one thermal storage device210 ​​containing at least one thermal storage medium, and

[0056] - at least one electric heating device220 of the thermal storage medium.

[0057] In the embodiment shown, the thermal storage medium is solid. The second electric heating system 20 then comprises a bypass circuit 200 of the combustion gas supply line 3, this bypass circuit 200 passing through at least one thermal storage device 210, here a single one, containing a solid thermal storage medium. Furthermore, the heating device 220, typically an electric heating device, for example Joule effect or other, is mounted on a bypass line 202 connected to the bypass circuit 200 and mounted in parallel with the thermal storage device 210. Valves 204 and 206, mounted on the bypass circuit and the bypass line respectively, and a fan 208 ensure flow regulation and fluid circulation. Of course, the invention is not limited by the number and position of the valve(s) and / or fan(s).In particular, in an embodiment not shown, at least one electric heating device may be integrated with at least one thermal storage device. The bypass pipe 202 is then omitted.

[0058] In the embodiment shown, the combustion gas supply line 3 includes a third electric heating system 30, preferably an electric heating device, for example Joule effect or other, mounted in parallel with the second electric heating system 20. A valve 5 allows control of the gas flow circulating through the third electric heating system 30.

[0059] A management system 40 is configured to control the different heating systems 10, 20, 30. This management system 40 can in particular regulate the target temperature Tc of the combustion gas circulating in the supply line 3 downstream of the heating systems 10, 20, 30 by regulating the electrical power supplied to each heating system and / or the flow rates circulating in the different lines.

[0060] The management system 40 can in particular be configured to: (a) in a charging phase in which the thermal storage medium of the second heating system 20 accumulates (stores) calories, operate the first heating system 10 to heat the gas to a first temperature T1, and (a1) operate the heating device 220 of the thermal storage medium to heat the latter, and / or (a2) use at least a fraction of the gas heated by the first heating system to heat the thermal storage medium, (b) in a discharging phase in which the thermal storage medium of the second heating system 20 releases calories, operate the first heating system 10 to heat the combustion gas to a second temperature T2,then circulate the entire combustion gas flow in the bypass circuit 200 through the thermal storage device 210 containing the thermal storage medium to heat the combustion gas from the second temperature T2 to a predetermined temperature Tp, or circulate a fraction of the gas flow at the second temperature T2 in the bypass circuit 200 through the thermal storage device containing the solid medium to heat this gas fraction to a third temperature T3, which, mixing with the remaining fraction of gas flow (at temperature T2) reaches the predetermined temperature Tp.

[0061] Specifically, during the charging phase, in the example shown, the management system 40 can be configured to circulate the combustion gas in the loop (here closed) comprising the heating device 220 and the storage device 210. Valve 204 is then closed, valve 206 is open, and the fan 208 ensures the circulation of the combustion gas through the heating device and then the storage device 210. The thermal storage medium in this device can then accumulate heat. The charging phase can advantageously be implemented for a sufficiently long period to reach a temperature in the thermal storage device preferably higher than the desired target temperature Tc of the combustion gas, for example, a temperature of 300 to 1000 °C, or 560 to 700 °C.

[0062] This charging phase can advantageously be implemented while electricity is cheaper and / or comes from decarbonized sources (wind, solar, nuclear power plant, hydroelectric, etc.), which makes it possible to decarbonize the electrical consumption of the installation and / or reduce operating costs.

[0063] During the charging phase, the first and third electric heating systems operate to heat the combustion gas to the desired target temperature Tc, typically from 200 to 700 °C, preferably from 300 to 600 °C.

[0064] Alternatively, or in combination, during the charging phase, the management system 40 can be configured to operate the first heating system 10 to heat the gas to the first temperature T1 and circulate a fraction of the gas through the circuit 200, which includes the storage device 210, to heat the thermal storage medium. In this case, depending on the configuration of the first heating device and the first temperature T1 to which it can heat the gas, the heating device 220 could be omitted (for example, when the first temperature T1 is higher than a desired storage temperature Ts).

[0065] During the discharge phase, valve 206 is closed and fan 208 is stopped. Valve 204 is open. Valve 5 can be fully closed and, optionally, the third electric heating system can be switched off. The combustion gas is then heated to the predetermined temperature Tp or target temperature Tc desired by the first and second electric heating systems. Valve 5 might not be fully closed, and the electric heating system 30 could operate at a lower power than during the load phase.

[0066] It is thus understood that, in this discharge phase, the total electrical power required to heat the combustion gas is reduced compared to the charging phase thanks to the calories supplied by the thermal storage device.

[0067] The invention is not limited to the embodiment shown. In particular, the third electric heating system 30 could be omitted and, if the heat pump PACH does not have sufficient power to heat the combustion gas to the desired temperature, one or more electric heating devices can be added to the first electric heating system, mounted in series and / or in parallel downstream and / or upstream of the heat pump and upstream of the second electric heating system 20.

[0068] Solid thermal storage media, generally in the form of powder, particles, or solid blocks with open cavities and / or channels, advantageously offers suitable thermal storage capacities and / or is capable of achieving heat transfer rates appropriate for the intended use. This solid medium can, for example, be contained within an insulated enclosure. Suitable heat transfer solids include volcanic rocks or refractory materials, such as alumina. A thermal storage device containing volcanic rocks produced by Brenmiller Energy can be used. Alternatively, stacked refractory materials can be used; the storage device could, for example, be similar to a glass furnace regenerator and contain a stack of refractory materials, which could be cruciform, brick, bushel, or pot shapes.Electrically conductive refractory bricks can also be used, which can be heated by the circulation of gas and / or by an electric current passing through the bricks during the charging of the thermal storage (for example, Joule Hive Thermal Battery refractory bricks).

[0069] In a second embodiment, the thermal storage medium is a liquid. In this case, the second electric heating system may include a circuit through which the liquid medium circulates, the circuit comprising at least one thermal storage device and the heat exchanger.

[0070] A first example of implementing this embodiment is described with reference to [reference to figure]. In this embodiment, the second electric heating system 22 comprises a circuit 221 including a single thermal storage device 211. Furthermore, the heating device 220 for the liquid medium is installed on a bypass line 223 mounted in parallel with the thermal storage device 211. Valves 224, 225 are provided for the circulation of fluids in the circuit 221 and the bypass line 223. A heat exchanger 226 ensures the transfer of heat from the liquid medium to the combustion gas circulating in the line 3.

[0071] In the embodiment shown, the first electric heating system 10 comprises, connected in series, a heat pump 10 and an electric heating device 10. However, the invention is not limited to this embodiment, and one or more heat pumps (in series and / or in parallel) could be provided, followed by one, two, or three electric heating devices, or any other configuration enabling the desired combustion gas temperature to be reached, namely a combination of one or more heating devices connected in series and / or in parallel. The use of a heat pump is, however, preferred.

[0072] In this example, a third electric heating system30, for example an electric heating device, is provided downstream of the second electric heating system22. This third heating system could, however, be omitted.

[0073] During the charging phase, the management system 40 is then configured to accumulate calories in the storage device 211. For this purpose, valve 225 can be closed, and valve 224 opened so that the liquid medium flows from the heating device 220 to the storage device 211. The management system 40 also operates the first heating system 10 and possibly the third heating system 30 when present, to heat the combustion gas from the ambient temperature, for example 25 °C, to a target temperature Tc, for example from 200 to 700 °C, preferably from 300 to 600 °C, for example from 500 to 550 °C.

[0074] During the discharge phase, the control system 40 is configured so that the storage device 211 releases the heat it has accumulated to the combustion gas circulating in the supply line 3. For this purpose, for example, valve 224 is closed and valve 225 is opened to allow the liquid medium to flow from the storage device 211 to the heat exchanger 226. The first electric heating system 10, and possibly the third electric heating system 30, can then be unloaded. To this end, the control system 40 can operate the first heating system to heat the combustion gas to a second temperature T2, for example, lower than the first temperature T1 of the charging phase.In the example, we can, for instance, maintain the operation of the PACH or reduce the electrical power supplied to the PACH, and stop the electric heating device Res_1, the missing calories being supplied by the second heating system20, and optionally by the third heating system30.

[0075] The liquid medium can advantageously be chosen from ionic liquids, salts such as potassium nitrate (KNO3), calcium nitrate (Ca(NO3)2), sodium nitrate (NaNO3), sodium nitrite (NaNO2), and lithium nitrate, alone or in mixtures, such as a mixture of sodium nitrate and potassium nitrate or a eutectic mixture of sodium nitrate and potassium nitrate, and salt-water systems in which the salts form hydrates, such as lithium bromide. Preferably, the liquid medium can be chosen from salts such as potassium nitrate, calcium nitrate, sodium nitrate, sodium nitrite, and lithium nitrate, alone or in mixtures.For example, one could use a eutectic mixture containing 60% by mass of sodium nitrate and 40% by mass of potassium nitrate (KNO3), also called "Solar Salt", or a mixture containing 7% by mass of NaNO3, 53% by mass of KNO3 and 40% by mass of NaNO2, or even a mixture containing 48% by mass of Ca(NO3)2, 45% of KNO3 and 7% of NaNO2.

[0076] The storage device 211 may further include a solid thermal storage medium, for example, volcanic rock, refractory bricks, or other materials, or may not. The storage device enclosure, which receives the liquid thermal storage medium and optionally a solid thermal storage medium, may contain layers of thermal storage media at different temperatures, with the temperature of the layers increasing from bottom to top. When a solid thermal storage medium is present, it may be placed in the lower part of the enclosure to form a bed. This type of storage device can reduce the amount of liquid thermal storage medium required. During charging, the liquid medium is drawn from the bottom of the enclosure and reinjected hot at the top. During discharging, the liquid medium exiting the top of the enclosure is sent directly to the heat exchanger.When a solid medium is present, it can be as previously described.

[0077] In this embodiment, the second electric heating system 22 comprises a first thermal storage device 211 and a second thermal storage device 212 mounted on the circuit 221. The thermal heating device 220 is disposed between the two thermal storage devices 211, 212 on the opposite side from the heat exchanger 226, as shown. A valve 227 allows control of the circulation of the liquid medium.

[0078] Thus, during the charging phase, the management system 40 can be configured to circulate the liquid medium from one thermal storage device to another, generally from the coldest to the hottest, passing through the heating device 220, for example by closing the valve 227, thereby allowing the heat to be accumulated in the second storage device 212 and heated to the storage temperature Ts. During the discharging phase, the management system 40 can then be configured to circulate the liquid medium from the second storage device 212 at the storage temperature Ts to the heat exchanger 226 before returning it to the first storage device 211, for example by opening the valve 227. The first and third heating systems 10 and 30 can be controlled by the management system 40 as previously described with reference to the.

[0079] The embodiment shown differs from that shown in Figure 1 by the position of the heating device 220 of the second electric heating device 24, which is installed not on the circuit 221 but on the combustion gas supply line 3. With this arrangement, it is the combustion gas circulating in the supply line 3 that, via the heat exchanger 226, heats the liquid medium circulating between the two thermal storage devices 211, 212 during the charging phase. Thus, the control system 40 can be configured to operate the heating device 220 only during the charging phase, this heating device 220 being off during the discharging phase.When the temperature of the gases exiting the heat exchanger is higher than the target temperature Tc, it may be advantageous to provide a bypass line that takes a fraction of the gas flow upstream of the heating device 220 and reinjects it into the line 3 downstream of the heat exchanger 226. The first and third heating systems 10 and 30 can be controlled by the management system 40 as previously described with reference to the.

[0080] Alternatively, only one of the two storage devices 211, 212 could be provided. Alternatively, or in combination, the heating device 220 and the heating device Res_1 could form a single heating device.

[0081] In the embodiments shown in Figures 2 to 4, the presence of the third electric heating system 30 downstream of the heat exchanger 226 of the second electric heating system 22, 24 is particularly advantageous when the liquid medium circulating in or present within the heat exchanger 226 must be maintained at a minimum temperature to prevent solidification during a charging phase. This third electric heating system 30 will then preferably be located as close as possible to the heat exchanger 226, downstream of it. Similarly, the heat exchanger 226 may preferably be located immediately downstream of a component of the first electric heating system 10, particularly in the embodiments of Figures 2 and 3, or immediately downstream of the heating device 220, in order to maintain the liquid medium circulating in or present within the heat exchanger 226 at a minimum temperature.

[0082] In the embodiments shown in Figures 3 and 4, the thermal storage devices and the liquid medium can be as described with reference to the.

[0083] The circuit 221 and the bypass pipe 223 may be equipped with one or more valve(s) and / or pump(s) to ensure the circulation of the liquid medium during the charging and discharging phases of the second electric heating system 22 or 24.

[0084] Regardless of the embodiment, the management system40 can also receive various pieces of information from one or more appropriately arranged sensors relating to:

[0085] - to the energy supply (electrical and / or thermal) of the heat pump (amount of current received and consumed, temperature and / or flow rate of the fluids whose temperature is controlled),

[0086] - the charging and discharging state of each thermal storage system (temperature of the thermal storage devices),

[0087] - to the phase in which each thermal storage system is located (charging, discharging),

[0088] - to the amount of electrical and / or thermal energy received / produced by each electric heating system (quantity of current, flow rate and / or temperature of fluids).

[0089] The management system 40 typically includes output or input / output interfaces. These may be wireless communication interfaces (Bluetooth, Wi-Fi, or other) or connectors (network port, USB port, serial port, FireWire® port, SCSI port, or other). These input and / or output interfaces can form communication means, optionally bidirectional, between the management system and the components of the electric heating systems used in the present invention.

[0090] The management system may also include storage means such as random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), flash memory, external memory, or other storage devices. These storage means can, among other things, store received data, measured values, calculated values, and one or more computer programs.

[0091] The steam cracking furnace 110 according to the invention is typically installed in a steam cracking installation 100.

[0092] Thus, the effluent exiting the steam cracking furnace 110 is then rapidly cooled (quenched) in one or more cooling units, then purified and separated in compression and fractionation units. These different units of a steam cracking plant are well known to those skilled in the art and will be briefly described below.

[0093] Typically, at the outlet of the steam cracking furnace reactor(s) 110, the cracked gases are vented to a rapid cooling unit comprising one or more heat exchangers (often designated by the acronyms TLE or TLX for "Transfer Line Exchanger"), in which the cracked gases are cooled, for example from 820-850°C to 300-510°C. These cooled cracked gases can optionally be fed to a fractionation column (also called primary fractionation) to condense and separate the fuel oil fraction from the cracked gas.

[0094] The fractionated overhead gases are brought to a second cooling unit, usually a water-quench tower, which allows most of the dilution vapor and heavy fuels present in the gases to condense.

[0095] At the outlet of the second cooling unit, the cracked gases enter a compression unit typically comprising a series of compression stages, usually three to six, each stage including a compressor, a cooling system (e.g., a heat exchanger), and a liquid-gas separation device. The compressors of the various stages are generally powered by a steam turbine or an electric motor (or a combination of these). This compression unit also includes a purification section to remove acidic gases (CO2, H2S, SO2) and a drying section to remove residual water. Between the compression stages, condensed water and light gasoline are removed.

[0096] The gases exiting the compression unit enter the third cooling unit where they are cooled to cryogenic temperatures. Cooling is typically provided by cryogenic fluids such as liquid ethylene and propylene.

[0097] The third cooling unit thus comprises refrigeration cycles using some of the propylene and ethylene produced as refrigerants to perform the fractionation. The gases undergo several refrigeration cycles during which the refrigerants are produced by liquefaction through a compressor, then cooled in a heat exchanger, and then further cooled by expansion.The third cooling unit thus makes it possible to cool the cracked gases entering the fractionation unit and more particularly the cold fractionation section (often referred to as the cold box) of it (de-methanizer), typically in several stages using ethylene, propylene and methane / hydrogen as refrigerant: (1) cooling of the cracked gases to about -70 to -100°C using propylene and / or ethylene in several stages, followed each time by a separation of the condensed hydrocarbons which are injected into the de-methanizer, (2) cooling of the remaining gases to about -125°C using methane / hydrogen, followed by a separation of the condensed hydrocarbons and (3) cooling of the remaining gases to about -165°C using methane / hydrogen, followed by a separation of the condensed methane and producing a hydrogen stream of more than 90 vol% purity.This type of configuration corresponds to a "de-methanizer first" fractionation unit sequence. However, the invention is not limited to this configuration and can be adapted to other fractionation unit configurations, particularly "de-ethanizer first" or "de-propanizer first" configurations.

[0098] The fractionation unit typically comprises a cold fractionation section operating at low temperature to separate C1 / C2 hydrocarbons, followed by a hot fractionation section operating at higher temperature to separate C3 / C4 hydrocarbons. The fractionation unit may, for example, include a digester, a propane converter, and / or an ethane converter. The sequence of these fractionation units—digester, ethane converter, and propane converter—can vary depending on the thermal integration required and influences the design of the cryogenic cooling unit. The fractionation unit typically includes fractionation columns, heat exchangers, and pumps and valves to ensure fluid circulation.

[0099] In this fractionation unit, the cracked, cooled gases can thus be distilled in a de-methanizer where methane and dihydrogen are extracted, then in a de-ethanizer to recover acetylene, ethane and ethylene, then in a de-propanizer in which propylene, propadiene, methylacetylene and propane are recovered, and finally in a de-butanizer to recover butanes, butadiene and butenes. Example

[0100] Power calculations were performed for a combustion air supply line equipped with an electric heating system according to the invention, comprising a first electric heating system including a heat pump and two Joule-effect heating devices connected in series, a second system including two thermal storage devices as described with reference to [reference to relevant section], and a third electric heating system including a Joule-effect heating device. The heat pump receives a hot fluid at 80 °C, and its first heat exchanger provides a thermal power of 11 MWth, while its second heat exchanger provides a thermal power of 7 MWth. The heat pump operates continuously under the same conditions to heat the combustion gas from 110 to 200 °C. In load mode, the temperature of the storage device of the second electric heating system reaches 560 °C.The storage system comprises 2500 m³. 3 of Solar Salt, namely a eutectic mixture of 60% by mass of sodium nitrate and 40% by mass of potassium nitrate.

[0101] Table 1 shows the calculated power output of each element in nominal mode (second electric heating system off), in load mode of the second electric heating system, and in discharge mode of the second electric heating system. In discharge mode, the second electric heating system provides the same thermal power output as a Joule-effect heater, but without consuming electricity, resulting in a lower overall electrical power consumption.

[0102] [Table 1] Table 1 Nominal Mode Load Mode Discharge Mode Air Temperature at Heat Pump Inlet 110 °C 110 °C 110 °C Air Temperature at Heat Pump Outlet 200 °C 200 °C 200 °C Electrical Power Supplied to Heat Pump 4 MWe 4 MWe 4 MWe Thermal Power Supplied by First Joule Effect Device of First Electric Heating System 10 MWth 10 MWth 10 MWth Air Temperature at Outlet of First Joule Effect Device 280 °C 280 °C 280 °C Thermal Power Supplied by Second Joule Effect Device of First Electric Heating System 22 MWth 22 MWth 0 Air Temperature at Outlet of Second Joule Effect Device 464 °C 464 °C 280 °C Thermal Power Supplied by Second Electric Heating System 0 0 22 MWth Air Temperature at Outlet of Heat exchanger of the second electric heating system 464 °C 464 °C 464 °C Thermal power supplied by the Joule effect device of the third electric heating system 8 MWth 8 MWth 8 MWth Temperatureof the air exiting the third electric heating system 534 °C 534 °C 534 °C

Claims

Electric gas heating installation (1), in particular for a steam cracking furnace (110), characterized in that it comprises: - at least one gas supply line (3), and: - a first electric heating system (10), mounted on at least one gas supply line, - a second electric heating system with thermal storage (20, 22, 24) mounted on at least one gas supply line downstream of the first heating system (10) with respect to the gas flow, and comprising: - at least one thermal storage device (210, 211, 212) containing at least one thermal storage medium selected from a solid medium and a liquid medium, - optionally at least one heating device (220) for at least one thermal storage medium,and- according to a first configuration (i) a bypass circuit (200) of at least one gas supply line (3) passing through at least one thermal storage device (210) containing only at least one solid medium,-or according to a second configuration (ii) a heat exchanger (226) in which the liquid medium and the gas supplied by at least one supply line circulate, and a circuit (221) in which the liquid medium circulates, this circuit comprising at least one thermal storage device (211, 212) and the heat exchanger (226), the first electric heating system comprising at least one heat pump (HPP) connected on the one hand to the gas supply line (3) so as to transmit heat to it and on the other hand to a line (4) in which a hot fluid circulates so as to receive heat from the latter,the installation further comprising a management system for the first and second electric heating systems, configured to: (a) in a charging phase in which at least one thermal storage medium of the second heating system (20) accumulates heat, operate the first heating system to heat the gas to a first temperature T1, and (a1) operate the heating device (220) to heat at least one thermal storage medium, and / or (a2) use at least a fraction of the gas heated by the first heating system to heat the thermal storage medium, (b) in a discharging phase in which at least one thermal storage medium of the second heating system (20) releases heat, control the shutdown of the optional heating device, operate the first heating system (10) to heat the gas to a second temperature T2,and: in the first configuration (i) circulate the entire gas flow at the second temperature T2 in the bypass circuit (200) through the thermal storage device (210) containing the solid medium to heat the gas from the second temperature T2 to a predetermined temperature Tp, or circulate a fraction of the gas flow at the second temperature T2 in the bypass circuit through the thermal storage device containing the solid medium to heat this gas fraction to a third temperature T3, which, when mixed with the remaining fraction of the gas flow, reaches the predetermined temperature Tp, or in the second configuration (ii) circulate the liquid medium through at least one thermal storage device and then through the heat exchanger (226) to heat the gas from the second temperature T2 to the predetermined temperature Tp. Installation (1) according to claim 1, characterized in that the first electric heating system (10) further comprises one or more of the following components mounted in series and / or in parallel on at least one gas supply line (3): - a heat pump (HPH) connected on the one hand to the gas supply line (3) so as to transmit heat to it and on the other hand to a line (4) in which a hot fluid circulates so as to receive heat from the latter, - a mechanical vapor recompression system, comprising at least one mechanical steam compression stage, at least one first heat exchanger receiving steam produced by the at least one mechanical compression stage and connected to the gas supply line so as to transmit heat to it,a second heat exchanger receiving heat from a hot fluid and producing steam to supply at least one mechanical compression stage, - an electric heating device (Res_1). Installation (1) according to claim 1 or 2, characterized in that, in the first configuration, the second electric heating system (20) comprises: - the bypass circuit (200) comprising at least one thermal storage device (210) containing only the solid medium and, - at least one heating device (220) for the solid medium, optionally mounted on a bypass line (202) connected to the bypass circuit in parallel with at least one thermal storage device (210). Installation (1) according to claim 3, characterized in that it comprises a third electric heating system (30) mounted on at least one gas supply line (3) in parallel with the second electric heating system (20). Installation (1) according to claim 1 or 2, characterized in that, in the second configuration of the second electric heating system (20), the circuit (221) comprises a single thermal storage device (211) and a heating device (220) for the liquid medium, optionally mounted on a bypass line (223) mounted in parallel with the thermal storage device (211). Installation (1) according to claim 1 or 2, characterized in that, in the second configuration of the second electric heating system (20), the circuit (221) comprises, mounted in series in a direction of circulation of the liquid medium, a first thermal storage device (211), a second thermal storage device (212) and the heat exchanger (226), at least one heating device (220) of the liquid medium being integrated into each thermal storage device or disposed between the first and second thermal storage devices. Installation (1) according to claim 1 or 2, characterized in that, in the second configuration of the second electric heating system (20), the circuit (221) comprises, mounted in series in a direction of circulation of the liquid medium, a first thermal storage device (211), optionally a second thermal storage device (212), and the heat exchanger (220), and in that at least one heating device (220) of the liquid medium is mounted on at least one gas supply line (3), upstream of the heat exchanger (226) of the second heating system (20). Installation (1) according to any one of claims 5 to 7, characterized in that it comprises a third electric heating system (30) mounted on at least one gas circulation line downstream of the heat exchanger (226) of the second electric heating system (20). Steam cracking installation comprising a steam cracking furnace and an electrical gas heating installation (1) according to any one of the preceding claims, the steam cracking furnace comprising a radiation zone equipped with burners connected to at least one fuel gas supply line and to at least one oxidizing gas supply line (3) and the electrical gas heating installation (1) being mounted on at least one oxidizing gas supply line (3). A process for steam cracking hydrocarbons characterized in that it comprises: - a cracking step of a hydrocarbon feedstock carried out at a cracking temperature in a steam cracking plant according to claim 9, this cracking temperature being obtained by the combustion in the burners of the steam cracking furnace of a mixture of combustion gas and hot oxidizing gas, in which the heating of the oxidizing gas before its entry into the burners is carried out by the electric heating plant (1) and comprises: - supplying the first electric heating system (10) with oxidizing gas to be heated, and - in a charging phase in which the thermal storage medium of the second electric heating system (20) accumulates heat, operating the first heating system to heat the gas to a first temperature T1,and (a1) operate the heating device (220) to heat the thermal storage medium and / or (a2) use at least a fraction of the gas heated by the first heating system to heat the thermal storage medium, - in a discharge phase in which the thermal storage medium of the second heating system releases heat, command the shutdown of the optional heating device, operate the first heating system (10) to heat the combustion gas to a second temperature T2, and in the first configuration (i) circulate the entire combustion gas flow in the bypass circuit (200) through the thermal storage device (210) containing the solid medium and heat the gas from the second temperature T2 to a predetermined temperature Tp,or circulate a fraction of the gas flow at the second temperature T2 in the bypass circuit through the thermal storage device containing the solid medium to heat this gas fraction to a third temperature T3, which, in mixing with the remaining fraction of gas flow, reaches the predetermined temperature Tp, or in the second configuration (ii) circulate the liquid medium through at least one thermal storage device and then into the heat exchanger (226) to heat the combustion gas from the second temperature T2 to the predetermined temperature Tp.

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