EP4386067A1

EP4386067A1 - Heat integration in an olefins production process using an electrically heated gas in a steam cracker furnace

Info

Publication number: EP4386067A1
Application number: EP22386092.5A
Authority: EP
Inventors: Georgios Bellos; Michael Steindl; Henk Hagen; Wim KAMPERMAN; Reto Greter; Govert Gerardus Pieter Van Der Ploeg; Martijn LUNSHOF; Galen Coupe; Richard R. Cooper
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2024-06-19

Abstract

The invention relates to a process for producing olefins from a feed stream containing hydrocarbons by pyrolytic cracking of the hydrocarbons in a steam cracker furnace, said process comprising feeding the hydrocarbons-containing feed stream to a tube in the convection section of the steam cracker furnace; pre-heating the hydrocarbons-containing feed stream in the convection section; feeding the pre-heated hydrocarbons-containing feed stream to a tube in the radiant section of the steam cracker furnace; and heating and pyrolytic cracking the hydrocarbons-containing feed stream in the radiant section resulting in an effluent containing olefins, wherein: at least part of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace is provided through indirect heat exchange between an electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace; and at least part of the used electrically heated gas is electrically re-heated and then re-used in said pre-heating and/or said heating.

Description

Field of the invention

The present invention relates to heat integration in a process for producing olefins from a feed stream containing hydrocarbons by pyrolytic cracking of the hydrocarbons in a steam cracker furnace, using an electrically heated gas in said furnace.

Background of the invention

Pyrolytic cracking of hydrocarbons in a steam cracker furnace is a petrochemical process that is widely used to produce olefins (such as ethylene, propylene, butylenes and butadiene) and optionally aromatics (such as benzene, toluene and xylene). Such pyrolytic cracking is usually performed in the presence of dilution steam, which is referred to as "steam cracking". The feed stream to such pyrolytic cracking process may include one or more of ethane, propane, butane, liquefied petroleum gas (LPG), naphtha, hydrowax and recycled waste plastics oil. In such pyrolytic cracking process, the hydrocarbons-containing stream is converted under the influence of heat, and substantially in the absence of oxygen, into an olefins-containing effluent.
A steam cracker furnace comprises a convection section and a radiant section. When considering the direction of a hydrocarbons-containing feed stream through a steam cracker furnace, the convection section is located in an upstream part of the steam cracker furnace and the radiant section is located in a downstream part thereof. However, when considering the direction of the below-mentioned flue gas through a steam cracker furnace, the convection section is located in a downstream part of the steam cracker furnace and the radiant section is located in an upstream part thereof.
The convection section of a furnace generally comprises one or more tubes into which a hydrocarbon stream is introduced, in which tubes the hydrocarbons-containing stream is pre-heated by hot flue gas which is present outside these tubes and which arises from the radiant section, wherein heat exchange takes place through the walls of said tubes. Depending on the configuration, the convection section may additionally comprise one or more tubes into which steam or another fluid is introduced to optimize heat recovery from the flue gas.
The radiant section of a furnace comprises one or more burners wherein oxygen, e.g. as present in air, and a fuel are contacted and the fuel is combusted resulting in heat release, which heat is needed to effectuate the pyrolytic cracking of the hydrocarbon stream in one or more tubes which are also comprised within the radiant section and into which the pre-heated hydrocarbon stream from the convection section is introduced. Generally, the fuel used in said burners may comprise liquid or gaseous hydrocarbons. In specific, it may comprise a fuel gas which may comprise hydrogen and/or methane, such as an off-gas containing a variety of combustible gases comprising hydrogen and/or methane, such as those originating from the olefins-containing effluent from the radiant section of the steam cracker furnace.
Combustion of hydrocarbons in a fuel in the burners of a steam cracker furnace results in the production of a flue gas comprising primarily water and carbon dioxide. Generally, carbon dioxide from such flue gas may have to be emitted into the Earth's atmosphere and/or may have to be captured in another form thereby preventing such emission. A distinction can be made between Carbon Capture and Storage (CCS) and Carbon Capture and Use (CCU) which both involve carbon dioxide capture which is cumbersome, requiring additional equipment, and therefore relatively expensive. In addition, CCS further increases the general costs of chemicals manufacturing because of the required energy expenditure for compression and distribution to carbon dioxide storage.
Therefore, in view of the above, it is generally desired to reduce the total amount of above-mentioned fuel, in specific a fuel gas, needed to produce the desired olefins as contained in the olefins-containing effluent from the steam cracker furnace. A reduced fuel gas consumption results in that the amount of carbon dioxide formed in the burners of the steam cracker furnace relative to the amount of desired products (i.e. olefins and optionally aromatics) is decreased.
According to EP3725865A1 , which concerns a method of producing olefins, energy required for a hydrocarbons cracking step, wherein the temperature of the feed stream is increased to the cracking temperature, may be provided by electricity. According to EP3725865A1 , heat conventionally supplied as thermal energy by the combustion of a fuel (e.g. natural gas/fossil fuels) in a furnace may be replaced by electrical heating, including heating by passing a relatively hot inert gas or another medium over tubes containing a fluid to be heated, wherein the hot inert gas or the other medium is heated electrically. In specific, EP3725865A1 discloses pre-heating of the feed by passing hot inert gas or another medium over the tubes, and electrically heating the hot inert gas or other medium, as well as heating by passing a hot, inert gas or other hot medium over tubes of a cracking reactor, wherein the hot gas or heated medium is heated electrically. Still further, EP3725865A1 discloses that the electricity needed for this heating may be produced from a renewable energy source.
However, renewable, non-fossil energy resources, which may be used in providing electricity for heating a hydrocarbons-containing fluid in a steam cracking process, may be limited available (and hence relatively expensive), globally and/or locally. For example, such renewable resources may alternatively be needed to provide electricity for non-industrial purposes. Therefore, in view of the above, it is an objective of the present invention to reduce the total amount of electricity needed to produce the desired olefins as contained in the olefins-containing effluent from the steam cracker furnace. An important advantage of such reduced electricity consumption is that the amount of used electricity relative to the amount of desired products (i.e. olefins and optionally aromatics) is decreased.
Further, generally, it is an object of the present invention to provide such steam cracking process for the production of olefins from a hydrocarbons-containing feed stream, which process is technically advantageous, efficient and affordable, in particular a process which does not have one or more of the above-mentioned disadvantages. Such technically advantageous process would preferably result in a relatively low energy demand and/or relatively low capital expenditure.

Summary of the invention

Surprisingly, it was found that one or more of the above-mentioned objectives may be achieved by an indirect heat exchange in the steam cracker furnace between (i) the hydrocarbons-containing feed stream inside a tube in the convection section and/or the radiant section of the steam cracker furnace and (ii) an electrically heated gas outside that tube, resulting in a (pre-)heated feed stream, combined with recirculating the used electrically heated gas through electrical re-heating of that used gas and re-using the re-heated gas in the (pre-)heating of the hydrocarbons-containing feed stream, whereby advantageously less electricity is needed to provide the heat duty for performing the pyrolytic cracking process at the same desired process product output.
In other words, through the present invention, advantageously, a reduced amount of electricity relative to the amount of desired products (i.e. olefins and optionally aromatics) in the effluent from the steam cracker furnace is needed. Accordingly, in case the electricity is produced from a non-renewable, fossil energy resource, less carbon dioxide is formed and hence advantageously less carbon dioxide is emitted into the Earth's atmosphere and/or less carbon dioxide may have to be captured in another form preventing such emission, such as in above-mentioned CCS and CCU methods. Or, in case the electricity is produced from a non-fossil energy resource, advantageously a reduced amount of that non-fossil energy resource is needed which latter resource may be limited available.
In addition, in steam cracking processes it is important to keep the stack temperature the same in order to ensure that the overall thermal efficiency of the steam cracker furnace is not decreased. Gas used for heating a hydrocarbons-containing feed in a steam cracking process can be emitted into the Earth's atmosphere via the stack of a steam cracker furnace. By lowering the stack temperature through enhanced use of the heat, carried by said gas, in the steam cracking process, significant energy savings may be made since a colder gas is emitted into the Earth's atmosphere. However, by such change of the stack temperature, a previously optimized overall thermal efficiency of the steam cracker furnace may no longer be attained. On the contrary, in the present invention, advantageously, the temperature of the gas used in the steam cracking process (corresponding with the stack temperature), i.e. after said gas has been used in heating the hydrocarbons-containing feed stream in the convection section and/or the radiant section of the steam cracker furnace, may be kept the same, since in the present invention that gas is an electrically heated gas which after use is recirculated and need not be emitted into the Earth's atmosphere. In other words, advantageously, in the present invention the same stack temperature may still be achieved, just like in a case wherein a flue gas, obtained by combustion of a fuel gas, is used for said heating of the hydrocarbons-containing feed.
Accordingly, the present invention relates to a process for producing olefins from a feed stream containing hydrocarbons by pyrolytic cracking of the hydrocarbons in a steam cracker furnace,
said process comprising feeding the hydrocarbons-containing feed stream to a tube in the convection section of the steam cracker furnace; pre-heating the hydrocarbons-containing feed stream in the convection section; feeding the pre-heated hydrocarbons-containing feed stream to a tube in the radiant section of the steam cracker furnace; and heating and pyrolytic cracking the hydrocarbons-containing feed stream in the radiant section resulting in an effluent containing olefins, wherein:

at least part of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace is provided through indirect heat exchange between an electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace; and
at least part of the used electrically heated gas is electrically re-heated and then re-used in said pre-heating and/or said heating.

Detailed description of the invention

The process of the present invention comprises multiple steps. In addition, said process may comprise one or more intermediate steps between consecutive steps. Further, said process may comprise one or more additional steps preceding the first step and/or following the last step. For example, in a case where said process comprises steps a), b) and c), said process may comprise one or more intermediate steps between steps a) and b) and between steps b) and c). Further, said process may comprise one or more additional steps preceding step a) and/or following step c).
While the process of the present invention and the stream(s) or composition(s) used in said process are described in terms of "comprising", "containing" or "including" one or more various described steps and components, respectively, they can also "consist essentially of" or "consist of" said one or more various described steps and components, respectively.
In the context of the present invention, in a case where a stream or a composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100%.
Further, where upper and lower limits are quoted for a property then a range of values defined by a combination of any of the upper limits with any of the lower limits is also implied.
The present invention concerns a process for producing olefins from a feed stream containing hydrocarbons (herein also referred to as "hydrocarbons-containing feed stream" or "feed stream") by pyrolytic cracking of the hydrocarbons in a steam cracker furnace.
The above-mentioned steam cracker furnace comprises a convection section and a radiant section. As explained in the introduction, when considering the direction of the above-mentioned feed stream through a steam cracker furnace, the convection section is located in an upstream part of the steam cracker furnace and the radiant section is located in a downstream part thereof.
The present process comprises a number of steps. Said process comprises feeding the hydrocarbons-containing feed stream to a tube in the convection section of the steam cracker furnace; pre-heating the hydrocarbons-containing feed stream in the convection section; feeding the pre-heated hydrocarbons-containing feed stream to a tube in the radiant section of the steam cracker furnace; and heating and pyrolytic cracking the hydrocarbons-containing feed stream in the radiant section resulting in an effluent containing olefins and optionally aromatics.
Within the present specification, "pre-heating" refers to heating a stream before introducing such stream into the radiant section of the steam cracker furnace.
Within the present specification, pre-heating and heating through indirect heat exchange refers to all pre-heating and heating which is not carried out by direct heat exchange, which direct heat exchange involves direct contact between the heating medium (e.g. a heated gas) and the medium to be heated (i.e. the hydrocarbons-containing feed stream).
Within the present specification, a "tube in the convection section" refers to a tube suitable for carrying a flow of fluid, such as a gas or a liquid, in which tube the hydrocarbons-containing feed stream is pre-heated.
Within the present specification, a "tube in the radiant section" refers to a tube suitable for carrying a flow of a gas, in which tube the pre-heated hydrocarbons-containing feed stream is further heated and pyrolytically cracked.
In the present invention, at least part of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace is provided through indirect heat exchange between an electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace.
Further, in the present invention, at least part of the used electrically heated gas is electrically re-heated and then re-used in pre-heating the hydrocarbons-containing feed stream in the convection section and/or heating the hydrocarbons-containing feed stream in the radiant section. This means that in the present invention, at least part of the electrically heated gas, after having been used in pre-heating the hydrocarbons-containing feed stream in the convection section and/or heating the hydrocarbons-containing feed stream in the radiant section, is recirculated. In this way, advantageously, residual heat that is still present in the used electrically heated gas, does not get lost by emitting it into the Earth's atmosphere. Through re-use of the re-heated gas in the (pre-)heating of the hydrocarbons-containing feed stream in the present invention, advantageously less electricity is needed to provide the heat duty for performing the pyrolytic cracking process at the same pyrolytic cracking process product output.
In the present invention, at least part of pre-heating of the hydrocarbons-containing feed stream in the convection section and/or at least part of heating of the hydrocarbons-containing feed stream in the radiant section is carried out through indirect heat exchange with an electrically heated gas which flows outside the tube in the convection section or the radiant section. First of all, this means that in the present invention, the electrically heated gas may be used (i) to pre-heat in the convection section only, or (ii) to heat in the radiant section only, or (iii), preferably, both to pre-heat in the convection section and to heat in the radiant section. Secondly, this implies that in addition to said indirect heat exchange with an electrically heated gas, heat exchange may also be effectuated in another way, for example by means of direct heat exchange (e.g. by adding dilution steam to the hydrocarbons-containing feed stream) and/or by means of indirect heat exchange not involving said indirect heat exchange with an electrically heated gas.
It is preferred in the present invention that the electrically heated gas outside the tube flows in a direction opposite to the direction in which the hydrocarbons-containing feed stream inside the tube flows. Hence, in case the hydrocarbons-containing feed stream flows downwardly, it is preferred that the electrically heated gas flows upwardly. Said indirect heat exchange implies a heat transfer from the electrically heated gas present in the convection section or radiant section outside a tube in that same section, to the hydrocarbons-containing feed stream as fed into said tube.
If in the present invention, the electrically heated gas is used to heat the hydrocarbons-containing feed stream in the radiant section, then after such use, the used electrically heated gas may be sent to the convection section and then be used in pre-heating the hydrocarbons-containing feed stream in the convection section, after which the used electrically heated gas is recirculated to the radiant section in accordance with the present invention. The foregoing corresponds with above-mentioned preferred option (iii) wherein the electrically heated gas is used both to pre-heat in the convection section and to heat in the radiant section.
Alternatively, the electrically heated gas used in the radiant section may not be sent to the convection section. In the latter case, the radiant section may also be referred to as a "stand-alone" radiant section and the convection section as a "stand-alone" convection section. In the case of a "stand-alone" radiant section, any electrically heated gas used in the radiant section is not sent to the convection section but recirculated to the radiant section in accordance with the present invention. Likewise, in the case of a "stand-alone" convection section, any electrically heated gas used in the convection section is not recirculated to the radiant section but to the convection section in accordance with the present invention.
In the present invention, the electrical heating of the gas to be used for (pre-)heating the hydrocarbons-containing feed stream, through indirect heat exchange in accordance with the present invention, may be performed by any electrical means. Further, said electrical heating may be performed externally (i.e. outside the steam cracker furnace) and/or internally (i.e. inside the steam cracker furnace). Preferably, said electrical heating is performed externally. Still further, the electricity needed for electrically heating the heated gas may be produced from a renewable and/or non-carbon dioxide emitting energy source. Said source may comprise wind, solar, geothermal, hydroelectric, nuclear, tidal, wave, or a combination thereof.
In the present invention, the gas to be used in (pre-heating the hydrocarbons-containing feed stream may comprise any gas that is capable of being electrically heated and subsequently transfer its heat to said stream through indirect heat exchange. Preferably, the electrically heated gas comprises one or more inert gases. The electrically heated gas may comprise one or more of air, nitrogen (N₂), water vapor and carbon dioxide (CO₂). Preferably, the electrically heated gas comprises air or nitrogen. More preferably, the electrically heated gas comprises air. In specific, it is most preferred that the electrically heated gas comprises air and carbon dioxide.
In accordance with the present invention, at least part of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace, is provided through indirect heat exchange between an electrically heated gas and the hydrocarbons-containing feed stream. At least 20% or at least 50% or at least 70% or at least 90% or at least 95% or at least 99% or, preferably, all (100%) of said energy may be provided through indirect heat exchange between the electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace.
Further, in accordance with the present invention, at least part of the used electrically heated gas is electrically re-heated and then re-used in pre-heating and/or heating the hydrocarbons-containing feed stream in the convection section and/or the radiant section, respectively, of the steam cracker furnace. At least 90% or at least 93% or at least 95% or at least 97% or at least 99% or at least 99.5% or at least 99.9% or, preferably, all (100%) of said used electrically heated gas may be recirculated in said way involving electrical re-heating and re-use. In case less than 100% of said used electrically heated gas is recirculated in said way, the remaining non-recirculated part may be vented, for example removed or purged from a circulation loop used for said recirculation, either continuously or intermittently. Advantageously, in this way, any build-up of possible contaminants may be prevented.
In conventional steam cracker furnaces, wherein flue gas resulting from the combustion of fuel gas with oxygen is used in (pre-)heating the hydrocarbons-containing feed stream, it is known to recirculate part of the used flue gas to the radiant section of the steam cracker furnace. See for example WO2021052642 and WO2018229267 . In said WO2018229267 , it is mentioned that an adiabatic flame temperature in the radiant section of the cracking furnace system is controlled by recirculating at least part of the flue gas, and that a higher adiabatic flame temperature may result in higher NOx production. Furthermore, only a relatively small part of used flue gas can be recirculated, as in conventional steam cracker furnaces the used flue gas is depleted of oxygen and additional fuel gas needs to be combusted with additional oxygen so as to generate additional heat in the form of hot flue gas. As a consequence, since either all or a relatively large part of the used flue gas needs to be removed in a conventional steam cracker furnace, there is a relatively high heat loss from the stack of that steam cracker furnace. With the present invention using an electrically heated gas for (pre-)heating the hydrocarbons-containing feed stream, such high heat loss is surprisingly and advantageously prevented or minimized by recirculation of used electrically heated gas.
In the present invention, at feeding the electrically heated gas to the convection section of the steam cracker furnace, the temperature of the electrically heated gas may be of from 600 to 1300 °C. Said temperature suitably depends on the point of entry. Further, in the present invention, at feeding the electrically heated gas to the radiant section of the steam cracker furnace, the temperature of the electrically heated gas may be of from 800 to 1700 °C, suitably of from 1000 to 1700 °C. Said temperature suitably depends on the point of entry.
In the present invention, the electrically heated gas may be fed to the convection section and/or the radiant section of the steam cracker furnace in any way. The electrically heated gas is suitably fed to the internal space within the steam cracker furnace which surrounds the tube or tubes containing the hydrocarbons-containing feed stream which needs to be (pre-)heated. There may be one or more inlets for feeding the electrically heated gas to the steam cracker furnace. In case there are multiple inlets, all of the gas fed via these multiple inlets may be electrically heated by means of one external electrical heating device (i.e. located outside the steam cracker furnace). Within the present specification, a single "electrical heating device" may comprise one electrical heater or multiple electrical heaters arranged in parallel and/or in series. After said electrical heating, a single gas feed stream is then split and the split substreams are fed to the multiple inlets. Alternatively, before heating, the gas feed stream may be split and the split substreams may be electrically heated by means of separate external electrical heating devices and then fed to the multiple inlets. Further, in case there are multiple inlets, these inlets may be at the same position or at different positions. In case there are multiple inlets at different positions, electrically heated gas fed via one of these inlets may have a temperature different from that of electrically heated gas fed via another one of these inlets. The temperature of the electrically heated gas may be determined by the position of the inlet via which it is fed to the steam cracker furnace. Generally, the more upstream an electrically heated gas inlet is positioned, when considering the direction of a hydrocarbons-containing feed stream through a steam cracker furnace, the lower the temperature may be. In such way, advantageously, the temperature profile along the entire steam cracker furnace may be optimized where needed. Furthermore, heating substreams to different temperatures, including lower and higher temperatures and not only a single relatively high temperature, advantageously, may be more efficient and hence more cost effective. Multiple electrically heated gas containing feed streams having different temperatures may be provided by splitting the gas feed stream, electrically heating the split substreams to different temperatures by means of separate external electrical heating devices and feeding the heated substreams to the multiple inlets. Since in the present invention, electrically heated gas after use is recirculated involving electrical re-heating and re-use, used electrically heated gas from the convection section or the radiant section of the steam cracker furnace is sent to a circulation loop, wherein the gas stream may be split into multiple substreams and which loop may contain one or more external electrical heating devices. Further, said circulation loop may comprise a fan enabling gas flow through such circulation loop. Additionally, the internal space within the steam cracker furnace which surrounds the tube or tubes containing the hydrocarbons-containing feed stream, may contain one or more internal electrical heating devices (e.g. one or more electrical radiative heaters) which may further heat the electrically heated gas as fed to said internal space.
In the present invention, the hydrocarbons-containing feed stream may be pre-heated in the convection section of the steam cracker furnace to a temperature of from 300 to 800 °C, more preferably of from 500 to 700 °C, most preferably of from 550 to 700 °C.
Further, as mentioned above, in the present invention, the pre-heated hydrocarbons-containing feed stream from the convection section is fed to a tube in the radiant section of the steam cracker furnace, wherein heating and pyrolytic cracking of hydrocarbons in the feed stream is performed, resulting in an effluent containing olefins. The hydrocarbons-containing feed stream may be heated in the radiant section of the steam cracker furnace to a temperature of from 650 to 1000 °C, more preferably of from 700 to 900 °C, most preferably of from 750 to 850 °C.
The olefins-containing effluent leaving the radiant section is still hot and may be used, in the present invention, to transfer heat to one or more of different media or fluids, including boiler feed water (utility water), steam, a hydrocarbons-containing feed stream and molten salts, either separately or as a combination of different fluids.
In specific, in the present invention, at least a portion of the olefins-containing effluent from the radiant section may be used in a direct sense in pre-heating the hydrocarbons-containing feed stream outside the steam cracker furnace through indirect heat exchange between the feed stream and said effluent.
As mentioned above, in a steam cracker furnace pyrolytic cracking of hydrocarbons is performed in the presence of dilution steam, which is therefore referred to as "steam cracking". Further, said dilution steam is "process water" which, as opposed to "utility water", is added in the form of steam as a diluent to the hydrocarbons-containing feed stream itself. In the present invention, dilution steam may be pre-heated outside the steam cracker furnace, either electrically or against a fluid at a higher temperature.
The stream that is fed to the present process for producing olefins is a feed stream containing hydrocarbons. Said feed stream contains saturated hydrocarbons. In addition, it may contain unsaturated hydrocarbons. Further, before said feed stream is subjected to the present process, it may be gaseous or in liquid form. In specific, said feed stream may comprise one or more of dry gas, ethane, propane, butane, C4 raffinate, gas oil, liquefied petroleum gas (LPG), naphtha, hydrowax, recycled waste plastics oil, biobased naphtha and biobased diesel.
The steam cracking in the present process may be performed in any known way. Said cracking is performed at an elevated temperature, preferably in the range of from 650 to 1000 °C, more preferably of from 700 to 900 °C, most preferably of from 750 to 850 °C. The present process involves steam cracking hydrocarbons which means that the cracking is performed in the presence of steam. Said steam (also referred to as "dilution steam") may be added to the hydrocarbons-containing feed stream prior to entering the convection section or in the convection section. Steam present in the cracking zone acts as a diluent to reduce the hydrocarbon partial pressure and thereby enhance the olefin yield. Steam also reduces the formation and deposition of carbonaceous material or coke in the cracking zone. Steam cracking occurs in the absence of oxygen. The residence time at the cracking conditions is very short, suitably of from 0.05 to 0.8 second, more suitably of from 0.10 to 0.6 second.
From the steam cracker, a cracker effluent is obtained that may comprise aromatics (as produced in the cracking process) which may include one or more of benzene, toluene and xylene, and that comprises olefins which may include one or more of ethylene, propylene, butylenes and butadiene, and hydrogen, water and carbon dioxide. The specific products obtained depend on the composition of the feed, the hydrocarbon-to-steam ratio, the cracking temperature and the furnace residence time. The cracked products from the cracker are then passed through a system comprising one or more indirect heat exchangers, such system often referred to as a TLE ("transfer line exchanger"). If a TLE comprises multiple heat exchangers, they can be arranged in parallel and/or in series. Further, if multiple TLEs are used, they can be arranged in parallel and/or in series, preferably in series. By said TLEs, the temperature of the cracked products is reduced. In this way, the composition of the process gas may be rapidly frozen. The TLEs preferably cool the cracked products by reducing the temperature at the outlet of the TLE or the final TLE to a temperature in the range of from 150 to 700 °C.

Claims

A process for producing olefins from a feed stream containing hydrocarbons by pyrolytic cracking of the hydrocarbons in a steam cracker furnace,
said process comprising feeding the hydrocarbons-containing feed stream to a tube in the convection section of the steam cracker furnace; pre-heating the hydrocarbons-containing feed stream in the convection section; feeding the pre-heated hydrocarbons-containing feed stream to a tube in the radiant section of the steam cracker furnace; and heating and pyrolytic cracking the hydrocarbons-containing feed stream in the radiant section resulting in an effluent containing olefins, wherein:
at least part of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace is provided through indirect heat exchange between an electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace; and

at least part of the used electrically heated gas is electrically re-heated and then re-used in said pre-heating and/or said heating.
The process according to claim 1, wherein the electricity needed for electrically heating the heated gas is produced from a renewable and/or non-carbon dioxide emitting energy source.
The process according to claim 2, wherein the renewable and/or non-carbon dioxide emitting energy source comprises wind, solar, geothermal, hydroelectric, nuclear, tidal, wave, or a combination thereof.
The process according to any one of claims 1 to 3, wherein at least 90% or at least 95% or at least 99% of the energy used in pre-heating and heating the hydrocarbons-containing feed stream through indirect heat exchange in the steam cracker furnace is provided through indirect heat exchange between an electrically heated gas outside the tube and the hydrocarbons-containing feed stream inside the tube in the steam cracker furnace.
The process according to any one of claims 1 to 4, wherein at least 95% or at least 97% or at least 99% or at least 99.5% of the used electrically heated gas is electrically re-heated and then re-used in said pre-heating and/or said heating.
The process according to any one of claims 1 to 5, wherein the electrically heated gas comprises one or more inert gases.
The process according to any one of claims 1 to 6, wherein the electrically heated gas comprises one or more of air, nitrogen, water vapor and carbon dioxide.
The process according to claim 7, wherein the electrically heated gas comprises air and carbon dioxide.
The process according to any one of claims 1 to 8, wherein the hydrocarbons-containing feed stream is pre-heated in the convection section to a temperature of from 300 to 800 °C.
The process according to any one of claims 1 to 9, wherein the hydrocarbons-containing feed stream is heated in the radiant section to a temperature of from 650 to 1000 °C.